http://sourceware.org/bugzilla/show_bug.cgi?id=12818
Summary: gold linker failed to remove all dead code dependency
properly
Product: binutils
Version: 2.22 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: gold
AssignedTo: i...@airs.com
ReportedBy: grabli_2...@mail.ru
Initially reported as
https://bugzilla.novell.com/show_bug.cgi?id=694266
http://sourceware.org/bugzilla/show_bug.cgi?id=12772
I`ve found, that this bug applied to gold linker too:
----- test.cpp
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
extern "C" int __attribute__((visibility("default"))) func(char *ptr)
{
static const char g_const[] = { 1, 1, 0 };
memcpy(ptr, g_const, 3);
return 0;
}
extern "C" char *func2(char *ptr)
{
static char buf[4096];
if (!getcwd(buf, sizeof(buf)))
buf[0] = 0;
#define STR "test_string"
memcpy(ptr, STR, sizeof(STR));
return buf;
}
-----
gcc -O3 -c -fpic -shared -fdata-sections -ffunction-sections \
-fvisibility-inlines-hidden -fvisibility=hidden -o test.o test.cpp
gold -m elf_x86_64 -gc-sections -s -shared -o test.so test.o
readelf -s 5540450000000000.so
Symbol table '.dynsym' contains 7 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000270 23 FUNC GLOBAL DEFAULT 4 func
2: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND
_GLOBAL_OFFSET_TABLE_
3: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND getcwd
4: 0000000000001380 0 NOTYPE GLOBAL DEFAULT ABS _edata
5: 0000000000001380 0 NOTYPE GLOBAL DEFAULT ABS __bss_start
6: 0000000000001380 0 NOTYPE GLOBAL DEFAULT ABS _end
As we see - getcwd dependency not discarded properly.
Also I`ve note that this way I can get smallest shared object size - 1888
bytes,
while using
"gcc -O3 -Wl,-x,-gc-sections,-s -fpic -flto -shared -fdata-sections
-ffunction-sections -fvisibility-inlines-hidden -fvisibility=hidden -o test.o
test.cpp"
size is 4552, and without -flto:
"gcc -O3 -Wl,-x,-gc-sections,-s -fpic -shared -fdata-sections
-ffunction-sections -fvisibility-inlines-hidden -fvisibility=hidden -o test.o
test.cpp"
size is 6280
I assume something going not ringht.
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