157 lines
4.2 KiB
Diff
157 lines
4.2 KiB
Diff
@@ -, +, @@
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relocation
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- In general they are. But IRELATIVE relocations are sorted to come
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last, and PLT entries are not sorted accordingly.
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---
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sysdeps/linux-gnu/x86/arch.h | 11 +++++
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sysdeps/linux-gnu/x86/plt.c | 101 +++++++++++++++++++++++++++++++++++++++++-
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2 files changed, 111 insertions(+), 1 deletions(-)
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--- a/sysdeps/linux-gnu/x86/arch.h
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+++ a/sysdeps/linux-gnu/x86/arch.h
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@@ -19,6 +19,10 @@
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
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* 02110-1301 USA
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*/
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+#ifndef LTRACE_X86_ARCH_H
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+#define LTRACE_X86_ARCH_H
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+
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+#include "vect.h"
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#define BREAKPOINT_VALUE {0xcc}
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#define BREAKPOINT_LENGTH 1
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@@ -30,9 +34,16 @@
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#define ARCH_HAVE_ADD_PLT_ENTRY
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+#define ARCH_HAVE_LTELF_DATA
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+struct arch_ltelf_data {
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+ struct vect plt_map;
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+};
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+
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#ifdef __x86_64__
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#define LT_ELFCLASS ELFCLASS64
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#define LT_ELF_MACHINE EM_X86_64
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#endif
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#define LT_ELFCLASS2 ELFCLASS32
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#define LT_ELF_MACHINE2 EM_386
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+
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+#endif /* LTRACE_X86_ARCH_H */
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--- a/sysdeps/linux-gnu/x86/plt.c
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+++ a/sysdeps/linux-gnu/x86/plt.c
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@@ -27,10 +27,19 @@
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#include "library.h"
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#include "trace.h"
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+static GElf_Addr
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+x86_plt_offset(uint32_t i)
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+{
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+ /* Skip the first PLT entry, which contains a stub to call the
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+ * resolver. */
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+ return (i + 1) * 16;
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+}
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+
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GElf_Addr
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arch_plt_sym_val(struct ltelf *lte, size_t ndx, GElf_Rela *rela)
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{
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- return lte->plt_addr + (ndx + 1) * 16;
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+ uint32_t i = *VECT_ELEMENT(<e->arch.plt_map, uint32_t, ndx);
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+ return x86_plt_offset(i) + lte->plt_addr;
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}
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void *
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@@ -62,3 +71,93 @@ arch_elf_add_plt_entry(struct process *proc, struct ltelf *lte,
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return PLT_DEFAULT;
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}
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+
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+int
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+arch_elf_init(struct ltelf *lte, struct library *lib)
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+{
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+ VECT_INIT(<e->arch.plt_map, unsigned int);
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+
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+ /* IRELATIVE slots may make the whole situation a fair deal
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+ * more complex. On x86{,_64}, the PLT slots are not
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+ * presented in the order of the corresponding relocations,
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+ * but in the order it which these symbols are in the symbol
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+ * table. That's static symbol table, which may be stripped
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+ * off, not dynsym--that doesn't contain IFUNC symbols at all.
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+ * So we have to decode each PLT entry to figure out what
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+ * entry it corresponds to. We need to interpret the PLT
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+ * table to figure this out.
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+ *
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+ * On i386, the PLT entry format is as follows:
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+ *
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+ * 8048300: ff 25 0c a0 04 08 jmp *0x804a00c
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+ * 8048306: 68 20 00 00 00 push $0x20
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+ * 804830b: e9 e0 ff ff ff jmp 80482f0 <_init+0x30>
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+ *
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+ * For PIE binaries it is the following:
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+ *
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+ * 410: ff a3 10 00 00 00 jmp *0x10(%ebx)
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+ * 416: 68 00 00 00 00 push $0x0
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+ * 41b: e9 d0 ff ff ff jmp 3f0 <_init+0x30>
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+ *
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+ * On x86_64, it is:
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+ *
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+ * 400420: ff 25 f2 0b 20 00 jmpq *0x200bf2(%rip) # 601018 <_GLOBAL_OFFSET_TABLE_+0x18>
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+ * 400426: 68 00 00 00 00 pushq $0x0
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+ * 40042b: e9 e0 ff ff ff jmpq 400410 <_init+0x18>
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+ *
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+ * On i386, the argument to push is an offset of relocation to
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+ * use. The first PLT slot has an offset of 0x0, the second
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+ * 0x8, etc. On x86_64, it's directly the index that we are
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+ * looking for.
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+ */
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+
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+ /* Here we scan the PLT table and initialize a map of
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+ * relocation->slot number in lte->arch.plt_map. */
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+
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+ size_t i;
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+ for (i = 0; i < vect_size(<e->plt_relocs); ++i) {
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+
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+ GElf_Addr offset = x86_plt_offset(i);
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+ uint32_t reloc_arg = 0;
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+
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+ uint8_t byte;
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+ if (elf_read_next_u8(lte->plt_data, &offset, &byte) < 0
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+ || byte != 0xff
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+ || elf_read_next_u8(lte->plt_data, &offset, &byte) < 0
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+ || (byte != 0xa3 && byte != 0x25))
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+ goto next;
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+
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+ /* Skip immediate argument in the instruction. */
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+ offset += 4;
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+
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+ if (elf_read_next_u8(lte->plt_data, &offset, &byte) < 0
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+ || byte != 0x68
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+ || elf_read_next_u32(lte->plt_data,
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+ &offset, &reloc_arg) < 0) {
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+ reloc_arg = 0;
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+ goto next;
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+ }
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+
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+ if (lte->ehdr.e_machine == EM_386) {
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+ if (reloc_arg % 8 != 0) {
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+ reloc_arg = 0;
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+ goto next;
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+ }
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+ reloc_arg /= 8;
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+ }
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+
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+ next:
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+ if (VECT_PUSHBACK(<e->arch.plt_map, &reloc_arg) < 0) {
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+ arch_elf_destroy(lte);
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+ return -1;
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+ }
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+ }
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+
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+ return 0;
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+}
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+
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+void
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+arch_elf_destroy(struct ltelf *lte)
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+{
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+ VECT_DESTROY(<e->arch.plt_map, uint32_t, NULL, NULL);
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+}
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--
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