https://sourceware.org/bugzilla/show_bug.cgi?id=26936
Bug ID: 26936
Summary: [ld, PIE] ld drops relocation for
.text.__x86.get_pc_thunk.bx
Product: binutils
Version: 2.35
Status: NEW
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: vries at gcc dot gnu.org
Target Milestone: ---
[ This is the ld variant of gdb PR26935. ]
Consider gcc testsuite test-case src/gcc/testsuite/gcc.dg/split-1.c.
When specifying -fsplit-stack, morestack.o is linked in, originating from
morestack.S in libgcc.
When specifying -m32 in combination with -fsplit-stack, morestack.o also
contains a function __x86.get_pc_thunk.bx, in section
.text.__x86.get_pc_thunk.bx.
So, when compiling like this:
...
$ gcc -g -fsplit-stack src/gcc/testsuite/gcc.dg/split-1.c -m32
...
we get in .debug_lines:
...
CU: libgcc/config/i386/morestack.S:
File name Line number Starting address View Stmt
morestack.S 109 0x8048a1e x
morestack.S 113 0x8048a1f x
...
morestack.S 832 0x8048b80 x
morestack.S 838 0x8048b85 x
morestack.S - 0x8048b86
morestack.S 636 0x8048880 x
morestack.S 637 0x8048883 x
morestack.S - 0x8048884
...
corresponding to:
...
08048a1e <__morestack_non_split>:
8048a1e: 50 push %eax
...
and:
...
08048880 <__x86.get_pc_thunk.bx>:
8048880: 8b 1c 24 mov (%esp),%ebx
...
Now, we compile in addition with -pie -fPIE, and get instead in .debug_lines:
...
CU: libgcc/config/i386/morestack.S:
File name Line number Starting address View Stmt
morestack.S 109 0xb8b x
morestack.S 113 0xb8c x
...
morestack.S 838 0xcf2 x
morestack.S - 0xcf3
morestack.S 636 0 x
morestack.S 637 0x3 x
morestack.S - 0x4
...
which matches with:
...
00000b8b <__morestack_non_split>:
b8b: 50 push %eax
...
but not with:
...
00000b87 <__x86.get_pc_thunk.ax>:
b87: 8b 04 24 mov (%esp),%eax
...
Looking at the relocations for .debug_line in morestack.o, we have:
...
Relocation section '.rel.debug_line' at offset 0x8f4 contains 2 entries:
Offset Info Type Sym. Value Symbol's Name
0000004e 00000101 R_386_32 00000000 .text
000000de 00000501 R_386_32 00000000
.text.__x86.get_pc_thunk.bx
...
matching with .debug_lines here:
...
Line Number Statements:
[0x0000004b] Extended opcode 2: set Address to 0x0
...
and:
...
[0x000000db] Extended opcode 2: set Address to 0x0
...
So, it looks like ld drops the second relocation in PIE mode.
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