https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82631
Bug ID: 82631
Summary: Bogus DW_AT_GNU_call_site_value
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: rafael.espindola at gmail dot com
Target Milestone: ---
Created attachment 42408
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42408&action=edit
testcase
If the attached file is compiled with "g++ test.cpp -fPIC -g -O3 -m32", the
produced dwarf has
DW_AT_location len 0x0001: 52: DW_OP_reg2
Which means an argument is begin passed in edx. It also has
DW_AT_GNU_call_site_value len 0x000e: 730003000000001c030000000022:
DW_OP_breg3+0 DW_OP_addr 0x00000000 DW_OP_minus DW_OP_addr 0x00000000
DW_OP_plus
The first DW_op_addr is
.long _GLOBAL_OFFSET_TABLE_
and the second one is
.long .LC0
The first line actually produces a R_386_GOTPC, so it looks like the expression
is computing
(ebx - (GOTEND - PC)) + LC0
The code using LC0 is
_Z3fn3Pi:
pushl %esi
pushl %ebx
xorl %ebx, %ebx
call __x86.get_pc_thunk.si
addl $_GLOBAL_OFFSET_TABLE_, %esi
subl $12, %esp
movl 24(%esp), %eax
leal .LC0@GOTOFF(%esi), %edx
pushl %ebx
movl %esi, %ebx
pushl %eax
call _ZL3fn2PiPKc1C.constprop.0
So at the point of the call ebx is GOTEND. This suggests that gcc is actually
trying to compute
(ebx - GOTEND) + LC0 but getting R_386_GOTPC wrong. But the expression also
simplifies to just LC0, which is what is actually in edx.
