------- Comment #3 from pinskia at gmail dot com 2009-03-18 14:22 -------
Subject: Re: New: [Mips] No space for arguments when implicitely calling
__get_tls_addr
Sent from my iPhone
On Mar 18, 2009, at 7:05 AM, "joel dot porquet at gmail dot com"
<gcc-bugzi...@gcc.gnu.org
> wrote:
> Mips ABI specifies to let the space for 4 arguments in stack when
> calling a
> function. This is not respected when accessing tls variable with a
> dynamic
> model: gcc implicitely calls __get_tls_addr without making rooms for
> the
> arguments. The top of the stack is then likely to be erase.
__get_tls_addr is a special function and does not have to follow that
part of the ABI but a different part which should be documented about
tls and dynamic tls.
>
> Here is an example:
>
> - test.c:
>
> extern void* __get_tls_addr(void*);
> extern __thread int a;
> void func(void)
> {
> a++;
> }
>
> Compiled and linked with:
>
> mipsel-unknown-elf-gcc -fpic -mshared -nostdinc -nostdlib -fno-
> builtin -mips2
> -EL -mabicalls -G0 -c -o test.o test.c
> mipsel-unknown-elf-ld -shared test.o -o test.so
>
> Result in assembly:
>
> 5ffe0390 <func>:
> 5ffe0390: 3c1c0001 lui gp,0x1
> 5ffe0394: 279c9090 addiu gp,gp,-28528
> 5ffe0398: 0399e021 addu gp,gp,t9
> 5ffe039c: 27bdffe8 addiu sp,sp,-24
> 5ffe03a0: afbf0014 sw ra,20(sp)
> 5ffe03a4: afbe0010 sw s8,16(sp)
> 5ffe03a8: afb0000c sw s0,12(sp)
> 5ffe03ac: 03a0f021 move s8,sp
> 5ffe03b0: afbc0000 sw gp,0(sp)
> 5ffe03b4: 8f99802c lw t9,-32724(gp)
> 5ffe03b8: 27848030 addiu a0,gp,-32720
> 5ffe03bc: 0320f809 jalr t9
> 5ffe03c0: 00000000 nop
> 5ffe03c4: 8fdc0000 lw gp,0(s8)
> 5ffe03c8: 8c420000 lw v0,0(v0)
> ...
>
> We can see than $gp is saved directly at the top of the stack
> 0($sp), and is
> likely to be erase in the callee function.
>
> A temporarily workaround is to insert a real function call in the
> same function
> which uses a tls variable.
> Example:
>
> extern void* __get_tls_addr(void*);
> extern __thread int a;
> static inline void fake(void){}
> void func(void)
> {
> fake();
> a++;
> }
>
> This result is then:
> 5ffe0390 <func>:
> 5ffe0390: 3c1c0001 lui gp,0x1
> 5ffe0394: 279c90c0 addiu gp,gp,-28480
> 5ffe0398: 0399e021 addu gp,gp,t9
> 5ffe039c: 27bdffd8 addiu sp,sp,-40
> 5ffe03a0: afbf0024 sw ra,36(sp)
> 5ffe03a4: afbe0020 sw s8,32(sp)
> 5ffe03a8: afb0001c sw s0,28(sp)
> 5ffe03ac: 03a0f021 move s8,sp
> 5ffe03b0: afbc0010 sw gp,16(sp)
> 5ffe03b4: 8f828018 lw v0,-32744(gp)
> 5ffe03b8: 24590418 addiu t9,v0,1048
> 5ffe03bc: 0320f809 jalr t9
> 5ffe03c0: 00000000 nop
> 5ffe03c4: 8fdc0010 lw gp,16(s8)
> ...
>
> We can now see that $gp is stored at 16($sp), which gives the
> required spare
> space for the 4 arguments in stack.
>
>
> --
> Summary: [Mips] No space for arguments when implicitely
> calling
> __get_tls_addr
> Product: gcc
> Version: 4.3.1
> Status: UNCONFIRMED
> Severity: normal
> Priority: P3
> Component: c
> AssignedTo: unassigned at gcc dot gnu dot org
> ReportedBy: joel dot porquet at gmail dot com
> GCC host triplet: i486-linux-gnu
> GCC target triplet: mipsel-unknown-elf
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39493
>
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39493
