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gcc/gcc-RHEL-105072-3.patch
Florian Weimer 54f65f0398 Exception handling performance improvements (RHEL-105072) 
Add a dependency on the GLIBC_2.35 glibc symbol set to libgcc, which
contains the definition of _dl_find_object.

Resolves: RHEL-105072
2025-07-30 16:42:47 +02:00

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commit 9488d24206687be80443dafdb2cdfc4ff3aca28c
Author: Florian Weimer <fweimer@redhat.com>
Date: Thu Nov 25 18:40:51 2021 +0100
libgcc: Split FDE search code from PT_GNU_EH_FRAME lookup
This allows switching to a different implementation for
PT_GNU_EH_FRAME lookup in a subsequent commit.
This moves some of the PT_GNU_EH_FRAME parsing out of the glibc loader
lock that is implied by dl_iterate_phdr. However, the FDE is already
parsed outside the lock before this change, so this does not introduce
additional crashes in case of a concurrent dlclose.
libgcc/ChangeLog:
* unwind-dw2-fde-dip.c (struct unw_eh_callback_data): Add hdr.
Remove func, ret.
(find_fde_tail): New function. Split from
_Unwind_IteratePhdrCallback. Move the result initialization
from _Unwind_Find_FDE.
(_Unwind_Find_FDE): Updated to call find_fde_tail.
diff --git a/libgcc/unwind-dw2-fde-dip.c b/libgcc/unwind-dw2-fde-dip.c
index 3f302826d2d49074..fbb0fbdebb92d484 100644
--- a/libgcc/unwind-dw2-fde-dip.c
+++ b/libgcc/unwind-dw2-fde-dip.c
@@ -113,8 +113,7 @@ struct unw_eh_callback_data
#if NEED_DBASE_MEMBER
void *dbase;
#endif
- void *func;
- const fde *ret;
+ const struct unw_eh_frame_hdr *hdr;
int check_cache;
};
@@ -197,10 +196,6 @@ _Unwind_IteratePhdrCallback (struct dl_phdr_info *info, size_t size, void *ptr)
#else
_Unwind_Ptr load_base;
#endif
- const unsigned char *p;
- const struct unw_eh_frame_hdr *hdr;
- _Unwind_Ptr eh_frame;
- struct object ob;
_Unwind_Ptr pc_low = 0, pc_high = 0;
struct ext_dl_phdr_info
@@ -348,10 +343,8 @@ _Unwind_IteratePhdrCallback (struct dl_phdr_info *info, size_t size, void *ptr)
return 0;
/* Read .eh_frame_hdr header. */
- hdr = (const struct unw_eh_frame_hdr *)
+ data->hdr = (const struct unw_eh_frame_hdr *)
__RELOC_POINTER (p_eh_frame_hdr->p_vaddr, load_base);
- if (hdr->version != 1)
- return 1;
#ifdef CRT_GET_RFIB_DATA
# if defined __i386__ || defined __nios2__
@@ -383,12 +376,30 @@ _Unwind_IteratePhdrCallback (struct dl_phdr_info *info, size_t size, void *ptr)
# endif
#endif
- _Unwind_Ptr dbase = unw_eh_callback_data_dbase (data);
+ return 1;
+}
+
+/* Find the FDE for the program counter PC, in a previously located
+ PT_GNU_EH_FRAME data region. *BASES is updated if an FDE to return is
+ found. */
+
+static const fde *
+find_fde_tail (_Unwind_Ptr pc,
+ const struct unw_eh_frame_hdr *hdr,
+ _Unwind_Ptr dbase,
+ struct dwarf_eh_bases *bases)
+{
+ const unsigned char *p = (const unsigned char *) (hdr + 1);
+ _Unwind_Ptr eh_frame;
+ struct object ob;
+
+ if (hdr->version != 1)
+ return NULL;
+
p = read_encoded_value_with_base (hdr->eh_frame_ptr_enc,
base_from_cb_data (hdr->eh_frame_ptr_enc,
dbase),
- (const unsigned char *) (hdr + 1),
- &eh_frame);
+ p, &eh_frame);
/* We require here specific table encoding to speed things up.
Also, DW_EH_PE_datarel here means using PT_GNU_EH_FRAME start
@@ -404,7 +415,7 @@ _Unwind_IteratePhdrCallback (struct dl_phdr_info *info, size_t size, void *ptr)
p, &fde_count);
/* Shouldn't happen. */
if (fde_count == 0)
- return 1;
+ return NULL;
if ((((_Unwind_Ptr) p) & 3) == 0)
{
struct fde_table {
@@ -419,9 +430,9 @@ _Unwind_IteratePhdrCallback (struct dl_phdr_info *info, size_t size, void *ptr)
_Unwind_Ptr range;
mid = fde_count - 1;
- if (data->pc < table[0].initial_loc + data_base)
- return 1;
- else if (data->pc < table[mid].initial_loc + data_base)
+ if (pc < table[0].initial_loc + data_base)
+ return NULL;
+ else if (pc < table[mid].initial_loc + data_base)
{
lo = 0;
hi = mid;
@@ -429,9 +440,9 @@ _Unwind_IteratePhdrCallback (struct dl_phdr_info *info, size_t size, void *ptr)
while (lo < hi)
{
mid = (lo + hi) / 2;
- if (data->pc < table[mid].initial_loc + data_base)
+ if (pc < table[mid].initial_loc + data_base)
hi = mid;
- else if (data->pc >= table[mid + 1].initial_loc + data_base)
+ else if (pc >= table[mid + 1].initial_loc + data_base)
lo = mid + 1;
else
break;
@@ -445,10 +456,16 @@ _Unwind_IteratePhdrCallback (struct dl_phdr_info *info, size_t size, void *ptr)
f_enc_size = size_of_encoded_value (f_enc);
read_encoded_value_with_base (f_enc & 0x0f, 0,
&f->pc_begin[f_enc_size], &range);
- if (data->pc < table[mid].initial_loc + data_base + range)
- data->ret = f;
- data->func = (void *) (table[mid].initial_loc + data_base);
- return 1;
+ _Unwind_Ptr func = table[mid].initial_loc + data_base;
+ if (pc < table[mid].initial_loc + data_base + range)
+ {
+ bases->tbase = NULL;
+ bases->dbase = (void *) dbase;
+ bases->func = (void *) func;
+ return f;
+ }
+ else
+ return NULL;
}
}
@@ -461,18 +478,20 @@ _Unwind_IteratePhdrCallback (struct dl_phdr_info *info, size_t size, void *ptr)
ob.u.single = (fde *) eh_frame;
ob.s.i = 0;
ob.s.b.mixed_encoding = 1; /* Need to assume worst case. */
- data->ret = linear_search_fdes (&ob, (fde *) eh_frame, (void *) data->pc);
- if (data->ret != NULL)
+ const fde *entry = linear_search_fdes (&ob, (fde *) eh_frame, (void *) pc);
+ if (entry != NULL)
{
_Unwind_Ptr func;
- unsigned int encoding = get_fde_encoding (data->ret);
+ unsigned int encoding = get_fde_encoding (entry);
read_encoded_value_with_base (encoding,
base_from_cb_data (encoding, dbase),
- data->ret->pc_begin, &func);
- data->func = (void *) func;
+ entry->pc_begin, &func);
+ bases->tbase = NULL;
+ bases->dbase = (void *) dbase;
+ bases->func = (void *) func;
}
- return 1;
+ return entry;
}
const fde *
@@ -489,24 +508,13 @@ _Unwind_Find_FDE (void *pc, struct dwarf_eh_bases *bases)
#if NEED_DBASE_MEMBER
data.dbase = NULL;
#endif
- data.func = NULL;
- data.ret = NULL;
data.check_cache = 1;
- if (dl_iterate_phdr (_Unwind_IteratePhdrCallback, &data) < 0)
+ if (dl_iterate_phdr (_Unwind_IteratePhdrCallback, &data) <= 0)
return NULL;
- if (data.ret)
- {
- bases->tbase = NULL;
-#if NEED_DBASE_MEMBER
- bases->dbase = data.dbase;
-#else
- bases->dbase = NULL;
-#endif
- bases->func = data.func;
- }
- return data.ret;
+ _Unwind_Ptr dbase = unw_eh_callback_data_dbase (&data);
+ return find_fde_tail ((_Unwind_Ptr) pc, data.hdr, dbase, bases);
}
#else
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