[llvm-bugs] [Bug 28306] New: Reference external functions without PLT
via llvm-bugs
llvm-bugs at lists.llvm.org
Sat Jun 25 16:08:57 PDT 2016
https://llvm.org/bugs/show_bug.cgi?id=28306
Bug ID: 28306
Summary: Reference external functions without PLT
Product: new-bugs
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: unassignedbugs at nondot.org
Reporter: hjl.tools at gmail.com
CC: david.l.kreitzer at intel.com, llvm-bugs at lists.llvm.org,
zia.ansari at intel.com
Classification: Unclassified
There are extensions to x86-64 psABI:
https://groups.google.com/forum/#!topic/x86-64-abi/de5_KnLHxtI
and i386 psABI:
https://groups.google.com/forum/#!topic/ia32-abi/awsRSvJOJfs
with alternate code sequences to reference external functions without
PLT:
[hjl at gnu-tools-1 pr67400]$ cat z.i
extern int bar (void);
int
foo (void)
{
return bar ();
}
[hjl at gnu-tools-1 pr67400]$ cat f.i
extern int name (void);
void *
ptr (void)
{
return name;
}
[hjl at gnu-tools-1 pr67400]$ cat t.i
static __thread int ld;
extern __thread int gd;
int *
get_ld (void)
{
return &ld;
}
int *
get_gd (void)
{
return &gd;
}
[hjl at gnu-tools-1 pr67400]$ make
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -O2 -fno-plt -S z.i
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -O2 -fno-plt -S f.i
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -O2 -fno-plt -fPIC -S t.i
[hjl at gnu-tools-1 pr67400]$ cat z.s
.file "z.i"
.text
.p2align 4,,15
.globl foo
.type foo, @function
foo:
.LFB0:
.cfi_startproc
jmp *bar at GOTPCREL(%rip)
.cfi_endproc
.LFE0:
.size foo, .-foo
.ident "GCC: (GNU) 7.0.0 20160625 (experimental)"
.section .note.GNU-stack,"", at progbits
[hjl at gnu-tools-1 pr67400]$ cat f.s
.file "f.i"
.text
.p2align 4,,15
.globl ptr
.type ptr, @function
ptr:
.LFB0:
.cfi_startproc
movq name at GOTPCREL(%rip), %rax
ret
.cfi_endproc
.LFE0:
.size ptr, .-ptr
.ident "GCC: (GNU) 7.0.0 20160625 (experimental)"
.section .note.GNU-stack,"", at progbits
[hjl at gnu-tools-1 pr67400]$ cat t.s
.file "t.i"
.text
.p2align 4,,15
.globl get_ld
.type get_ld, @function
get_ld:
.LFB0:
.cfi_startproc
subq $8, %rsp
.cfi_def_cfa_offset 16
leaq ld at tlsld(%rip), %rdi
call *__tls_get_addr at GOTPCREL(%rip)
addq $8, %rsp
.cfi_def_cfa_offset 8
addq $ld at dtpoff, %rax
ret
.cfi_endproc
.LFE0:
.size get_ld, .-get_ld
.p2align 4,,15
.globl get_gd
.type get_gd, @function
get_gd:
.LFB1:
.cfi_startproc
subq $8, %rsp
.cfi_def_cfa_offset 16
.byte 0x66
leaq gd at tlsgd(%rip), %rdi
.byte 0x66
rex64
call *__tls_get_addr at GOTPCREL(%rip)
addq $8, %rsp
.cfi_def_cfa_offset 8
ret
.cfi_endproc
.LFE1:
.size get_gd, .-get_gd
.section .tbss,"awT", at nobits
.align 4
.type ld, @object
.size ld, 4
ld:
.zero 4
.ident "GCC: (GNU) 7.0.0 20160625 (experimental)"
.section .note.GNU-stack,"", at progbits
[hjl at gnu-tools-1 pr67400]$ make
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -O2 -fno-plt -m32 -S z.i
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -O2 -fno-plt -m32 -S f.i
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -O2 -fno-plt -m32 -fPIC -S
t.i
[hjl at gnu-tools-1 pr67400]$ cat z.s
.file "z.i"
.text
.p2align 4,,15
.globl foo
.type foo, @function
foo:
.LFB0:
.cfi_startproc
jmp *bar at GOT
.cfi_endproc
.LFE0:
.size foo, .-foo
.ident "GCC: (GNU) 7.0.0 20160625 (experimental)"
.section .note.GNU-stack,"", at progbits
[hjl at gnu-tools-1 pr67400]$ cat f.s
.file "f.i"
.text
.p2align 4,,15
.globl ptr
.type ptr, @function
ptr:
.LFB0:
.cfi_startproc
movl name at GOT, %eax
ret
.cfi_endproc
.LFE0:
.size ptr, .-ptr
.ident "GCC: (GNU) 7.0.0 20160625 (experimental)"
.section .note.GNU-stack,"", at progbits
[hjl at gnu-tools-1 pr67400]$ cat t.s
.file "t.i"
.text
.p2align 4,,15
.globl get_ld
.type get_ld, @function
get_ld:
.LFB0:
.cfi_startproc
call __x86.get_pc_thunk.dx
addl $_GLOBAL_OFFSET_TABLE_, %edx
subl $12, %esp
.cfi_def_cfa_offset 16
leal ld at tlsgd(%edx), %eax
call *___tls_get_addr at GOT(%edx)
addl $12, %esp
.cfi_def_cfa_offset 4
ret
.cfi_endproc
.LFE0:
.size get_ld, .-get_ld
.p2align 4,,15
.globl get_gd
.type get_gd, @function
get_gd:
.LFB1:
.cfi_startproc
call __x86.get_pc_thunk.dx
addl $_GLOBAL_OFFSET_TABLE_, %edx
subl $12, %esp
.cfi_def_cfa_offset 16
leal gd at tlsgd(%edx), %eax
call *___tls_get_addr at GOT(%edx)
addl $12, %esp
.cfi_def_cfa_offset 4
ret
.cfi_endproc
.LFE1:
.size get_gd, .-get_gd
.section .tbss,"awT", at nobits
.align 4
.type ld, @object
.size ld, 4
ld:
.zero 4
.section
.text.__x86.get_pc_thunk.dx,"axG", at progbits,__x86.get_pc_thunk.dx,comdat
.globl __x86.get_pc_thunk.dx
.hidden __x86.get_pc_thunk.dx
.type __x86.get_pc_thunk.dx, @function
__x86.get_pc_thunk.dx:
.LFB2:
.cfi_startproc
movl (%esp), %edx
ret
.cfi_endproc
.LFE2:
.ident "GCC: (GNU) 7.0.0 20160625 (experimental)"
.section .note.GNU-stack,"", at progbits
[hjl at gnu-tools-1 pr67400]$
llvm should also implement -fno-plt.
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