Update mmap() flags and errors lists (RHEL-30823)
Resolves: RHEL-30823
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DJ Delorie
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glibc-RHEL-30823.patch
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glibc-RHEL-30823.patch
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From dce754b1553b86fc6352636f1fa490a85b7cf0ff Mon Sep 17 00:00:00 2001
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From: DJ Delorie <dj@redhat.com>
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Date: Fri, 10 May 2024 14:52:09 -0400
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Subject: Update mmap() flags and errors lists
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Extend the list of MAP_* macros to include all macros available
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to the average program (gcc -E -dM | grep MAP_*)
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Extend the list of errno codes.
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Reviewed-by: Florian Weimer <fweimer@redhat.com>
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diff --git a/manual/llio.texi b/manual/llio.texi
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index fe1807a849..78c7c79913 100644
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--- a/manual/llio.texi
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+++ b/manual/llio.texi
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@@ -1573,10 +1573,15 @@ permitted. They include @code{PROT_READ}, @code{PROT_WRITE}, and
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of address space for future use. The @code{mprotect} function can be
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used to change the protection flags. @xref{Memory Protection}.
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-@var{flags} contains flags that control the nature of the map.
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-One of @code{MAP_SHARED} or @code{MAP_PRIVATE} must be specified.
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+The @var{flags} parameter contains flags that control the nature of
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+the map. One of @code{MAP_SHARED}, @code{MAP_SHARED_VALIDATE}, or
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+@code{MAP_PRIVATE} must be specified. Additional flags may be bitwise
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+OR'd to further define the mapping.
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-They include:
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+Note that, aside from @code{MAP_PRIVATE} and @code{MAP_SHARED}, not
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+all flags are supported on all versions of all operating systems.
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+Consult the kernel-specific documentation for details. The flags
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+include:
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@vtable @code
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@item MAP_PRIVATE
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@@ -1598,9 +1603,19 @@ Note that actual writing may take place at any time. You need to use
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@code{msync}, described below, if it is important that other processes
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using conventional I/O get a consistent view of the file.
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+@item MAP_SHARED_VALIDATE
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+Similar to @code{MAP_SHARED} except that additional flags will be
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+validated by the kernel, and the call will fail if an unrecognized
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+flag is provided. With @code{MAP_SHARED} using a flag on a kernel
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+that doesn't support it causes the flag to be ignored.
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+@code{MAP_SHARED_VALIDATE} should be used when the behavior of all
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+flags is required.
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+
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@item MAP_FIXED
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This forces the system to use the exact mapping address specified in
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-@var{address} and fail if it can't.
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+@var{address} and fail if it can't. Note that if the new mapping
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+would overlap an existing mapping, the overlapping portion of the
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+existing map is unmapped.
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@c One of these is official - the other is obviously an obsolete synonym
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@c Which is which?
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@@ -1641,10 +1656,73 @@ The @code{MAP_HUGETLB} flag is specific to Linux.
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@c There is a mechanism to select different hugepage sizes; see
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@c include/uapi/asm-generic/hugetlb_encode.h in the kernel sources.
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-@c Linux has some other MAP_ options, which I have not discussed here.
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-@c MAP_DENYWRITE, MAP_EXECUTABLE and MAP_GROWSDOWN don't seem applicable to
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-@c user programs (and I don't understand the last two). MAP_LOCKED does
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-@c not appear to be implemented.
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+@item MAP_32BIT
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+Require addresses that can be accessed with a signed 32 bit pointer,
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+i.e., within the first 2 GiB. Ignored if MAP_FIXED is specified.
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+
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+@item MAP_DENYWRITE
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+@itemx MAP_EXECUTABLE
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+@itemx MAP_FILE
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+
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+Provided for compatibility. Ignored by the Linux kernel.
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+
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+@item MAP_FIXED_NOREPLACE
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+Similar to @code{MAP_FIXED} except the call will fail with
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+@code{EEXIST} if the new mapping would overwrite an existing mapping.
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+To test for support for this flag, specify MAP_FIXED_NOREPLACE without
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+MAP_FIXED, and (if the call was successful) check the actual address
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+returned. If it does not match the address passed, then this flag is
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+not supported.
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+
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+@item MAP_GROWSDOWN
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+This flag is used to make stacks, and is typically only needed inside
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+the program loader to set up the main stack for the running process.
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+The mapping is created according to the other flags, except an
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+additional page just prior to the mapping is marked as a ``guard
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+page''. If a write is attempted inside this guard page, that page is
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+mapped, the mapping is extended, and a new guard page is created.
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+Thus, the mapping continues to grow towards lower addresses until it
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+encounters some other mapping.
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+
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+Note that accessing memory beyond the guard page will not trigger this
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+feature. In gcc, use @code{-fstack-clash-protection} to ensure the
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+guard page is always touched.
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+
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+@item MAP_LOCKED
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+A hint that requests that mapped pages are locked in memory (i.e. not
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+paged out). Note that this is a request and not a requirement; use
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+@code{mlock} if locking is required.
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+
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+@item MAP_POPULATE
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+@itemx MAP_NONBLOCK
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+@code{MAP_POPULATE} is a hint that requests that the kernel read-ahead
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+a file-backed mapping, causing pages to be mapped before they're
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+needed. @code{MAP_NONBLOCK} is a hint that requests that the kernel
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+@emph{not} attempt such except for pages are already in memory. Note
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+that neither of these hints affects future paging activity, use
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+@code{mlock} if such needs to be controlled.
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+
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+@item MAP_NORESERVE
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+Asks the kernel to not reserve physical backing (i.e. space in a swap
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+device) for a mapping. This would be useful for, for example, a very
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+large but sparsely used mapping which need not be limited in total
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+length by available RAM, but with very few mapped pages. Note that
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+writes to such a mapping may cause a @code{SIGSEGV} if the system is
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+unable to map a page due to lack of resources.
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+
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+On Linux, this flag's behavior may be overwridden by
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+@file{/proc/sys/vm/overcommit_memory} as documented in the proc(5) man
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+page.
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+
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+@item MAP_STACK
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+Ensures that the resulting mapping is suitable for use as a program
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+stack. For example, the use of huge pages might be precluded.
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+
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+@item MAP_SYNC
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+This is a special flag for DAX devices, which tells the kernel to
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+write dirty metadata out whenever dirty data is written out. Unlike
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+most other flags, this one will fail unless @code{MAP_SHARED_VALIDATE}
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+is also given.
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@end vtable
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@@ -1655,6 +1733,24 @@ Possible errors include:
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@table @code
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+@item EACCES
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+
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+@var{filedes} was not open for the type of access specified in @var{protect}.
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+
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+@item EAGAIN
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+
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+The system has temporarily run out of resources.
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+
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+@item EBADF
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+
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+The @var{fd} passed is invalid, and a valid file descriptor is
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+required (i.e. MAP_ANONYMOUS was not specified).
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+
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+@item EEXIST
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+
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+@code{MAP_FIXED_NOREPLACE} was specified and an existing mapping was
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+found overlapping the requested address range.
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+
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@item EINVAL
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Either @var{address} was unusable (because it is not a multiple of the
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@@ -1663,23 +1759,37 @@ applicable page size), or inconsistent @var{flags} were given.
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If @code{MAP_HUGETLB} was specified, the file or system does not support
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large page sizes.
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-@item EACCES
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+@item ENODEV
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-@var{filedes} was not open for the type of access specified in @var{protect}.
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+This file is of a type that doesn't support mapping, the process has
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+exceeded its data space limit, or the map request would exceed the
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+process's virtual address space.
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@item ENOMEM
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-Either there is not enough memory for the operation, or the process is
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-out of address space.
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-
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-@item ENODEV
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-
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-This file is of a type that doesn't support mapping.
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+There is not enough memory for the operation, the process is out of
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+address space, or there are too many mappings. On Linux, the maximum
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+number of mappings can be controlled via
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+@file{/proc/sys/vm/max_map_count} or, if your OS supports it, via
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+the @code{vm.max_map_count} @code{sysctl} setting.
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@item ENOEXEC
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The file is on a filesystem that doesn't support mapping.
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+@item EPERM
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+
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+@code{PROT_EXEC} was requested but the file is on a filesystem that
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+was mounted with execution denied, a file seal prevented the mapping,
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+or the caller set MAP_HUDETLB but does not have the required
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+priviledges.
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+
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+@item EOVERFLOW
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+
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+Either the offset into the file plus the length of the mapping causes
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+internal page counts to overflow, or the offset requested exceeds the
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+length of the file.
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+
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@c On Linux, EAGAIN will appear if the file has a conflicting mandatory lock.
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@c However mandatory locks are not discussed in this manual.
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@c
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@ -155,7 +155,7 @@ end \
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Summary: The GNU libc libraries
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Name: glibc
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Version: %{glibcversion}
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Release: 115%{?dist}
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Release: 116%{?dist}
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# In general, GPLv2+ is used by programs, LGPLv2+ is used for
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# libraries.
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@ -837,6 +837,7 @@ Patch600: glibc-RHEL-39000-2.patch
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Patch601: glibc-RHEL-39000-3.patch
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Patch602: glibc-RHEL-39992-1.patch
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Patch603: glibc-RHEL-39992-2.patch
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Patch604: glibc-RHEL-30823.patch
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##############################################################################
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# Continued list of core "glibc" package information:
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@ -2995,6 +2996,9 @@ update_gconv_modules_cache ()
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%endif
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%changelog
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* Fri Jul 12 2024 DJ Delorie <dj@redhat.com> - 2.34-116
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- Update mmap() flags and errors lists (RHEL-30823)
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* Wed Jul 03 2024 Patsy Griffin <patsy@redhat.com> - 2.34-115
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- elf: Avoid some free (NULL) calls in _dl_update_slotinfo
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- elf: Support recursive use of dynamic TLS in interposed malloc (RHEL-39992)
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