* aarch64 inline asm / -fPIC problem
@ 2020-08-27 21:23 Joe Buehler
2020-08-28 13:45 ` Joe Buehler
2020-08-29 15:45 ` Andrew Haley
0 siblings, 2 replies; 7+ messages in thread
From: Joe Buehler @ 2020-08-27 21:23 UTC (permalink / raw)
To: gcc-help
My (compiler test) program:
int
main()
{
__asm__ volatile(".8byte %0\n\t" : : "i" ("message %s\n"));
return 0;
}
This compiles fine with gcc 4.3.3 MIPS using:
gcc -S -fPIC temp.c
It fails with gcc 7.3.0 aarch64. Output is:
temp.c: In function main :
temp.c:4:2: warning: asm operand 0 probably doesn t match constraints
__asm__ volatile(".8byte %0\n\t" : : "i" ("message %s\n"));
^~~~~~~
temp.c:4:2: error: impossible constraint in asm
Removing the -fPIC it will compile fine.
The relevant section of the MIPS generated code looks like this:
.rdata
.align 2
$LC0:
.ascii "message %s\012\000"
.text
.align 2
.globl main
.ent main
.type main, @function
main:
.set nomips16
.frame $fp,8,$31 # vars= 0, regs= 1/0, args= 0, gp= 0
.mask 0x40000000,-4
.fmask 0x00000000,0
addiu $sp,$sp,-8
sw $fp,4($sp)
move $fp,$sp
#APP
# 4 "temp.c" 1
.8byte $LC0
I am unable to code something similar manually using inline asm because
the string is a format string containing % characters, which inline asm
will of course try to interpret. (Does gcc provide anything to escape %
chars in a literal string?)
Any suggestions?
Joe Buehler
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: aarch64 inline asm / -fPIC problem
2020-08-27 21:23 aarch64 inline asm / -fPIC problem Joe Buehler
@ 2020-08-28 13:45 ` Joe Buehler
2020-08-28 15:17 ` Joe Buehler
2020-08-29 15:45 ` Andrew Haley
1 sibling, 1 reply; 7+ messages in thread
From: Joe Buehler @ 2020-08-28 13:45 UTC (permalink / raw)
Cc: gcc-help
I looked at the gcc 7.3.0 source and got a hint. Interestingly,
changing the constraint from "i" to "X" fixes the problem. Seems like a
gcc bug to me.
Joe Buehler
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: aarch64 inline asm / -fPIC problem
2020-08-28 13:45 ` Joe Buehler
@ 2020-08-28 15:17 ` Joe Buehler
0 siblings, 0 replies; 7+ messages in thread
From: Joe Buehler @ 2020-08-28 15:17 UTC (permalink / raw)
Cc: gcc-help
There are still some issues with this, "X" does not always work when I
compile real code. Sometimes it does, sometimes it doesn't.
Joe Buehler
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: aarch64 inline asm / -fPIC problem
2020-08-27 21:23 aarch64 inline asm / -fPIC problem Joe Buehler
2020-08-28 13:45 ` Joe Buehler
@ 2020-08-29 15:45 ` Andrew Haley
2020-09-02 18:25 ` aph@redhat.com Joe Buehler
2020-09-02 18:26 ` aarch64 inline asm / -fPIC problem Joe Buehler
1 sibling, 2 replies; 7+ messages in thread
From: Andrew Haley @ 2020-08-29 15:45 UTC (permalink / raw)
To: Joe Buehler, gcc-help
On 27/08/2020 22:23, Joe Buehler via Gcc-help wrote:
temp.c: In function main :
temp.c:4:2: warning: asm operand 0 probably doesn t match constraints
__asm__ volatile(".8byte %0\n\t" : : "i" ("message %s\n"));
^~~~~~~
temp.c:4:2: error: impossible constraint in asm
I'd use the "S" constraint.
> I am unable to code something similar manually using inline asm because
> the string is a format string containing % characters, which inline asm
> will of course try to interpret. (Does gcc provide anything to escape %
> chars in a literal string?)
"%%"
--
Andrew Haley (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: aph@redhat.com
2020-08-29 15:45 ` Andrew Haley
@ 2020-09-02 18:25 ` Joe Buehler
2020-09-03 10:18 ` aph@redhat.com Andrew Haley
2020-09-02 18:26 ` aarch64 inline asm / -fPIC problem Joe Buehler
1 sibling, 1 reply; 7+ messages in thread
From: Joe Buehler @ 2020-09-02 18:25 UTC (permalink / raw)
To: Andrew Haley; +Cc: gcc-help
Andrew Haley wrote:
> On 27/08/2020 22:23, Joe Buehler via Gcc-help wrote:
>
> temp.c: In function main :
> temp.c:4:2: warning: asm operand 0 probably doesn t match constraints
> __asm__ volatile(".8byte %0\n\t" : : "i" ("message %s\n"));
> ^~~~~~~
> temp.c:4:2: error: impossible constraint in asm
>
> I'd use the "S" constraint.
Thanks that worked.
>
>> I am unable to code something similar manually using inline asm because
>> the string is a format string containing % characters, which inline asm
>> will of course try to interpret. (Does gcc provide anything to escape %
>> chars in a literal string?)
>
> "%%"
>
The problem is that I have literal printf format strings in a multiplatform code base. I need something like a gcc builtin to do the % doubling.
#define X(fmt) asm ("lines " __builtin_escape(fmt) " more lines")
Joe Buehler
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: aarch64 inline asm / -fPIC problem
2020-08-29 15:45 ` Andrew Haley
2020-09-02 18:25 ` aph@redhat.com Joe Buehler
@ 2020-09-02 18:26 ` Joe Buehler
1 sibling, 0 replies; 7+ messages in thread
From: Joe Buehler @ 2020-09-02 18:26 UTC (permalink / raw)
To: Andrew Haley; +Cc: gcc-help
Andrew Haley wrote:
> On 27/08/2020 22:23, Joe Buehler via Gcc-help wrote:
>
> temp.c: In function main :
> temp.c:4:2: warning: asm operand 0 probably doesn t match constraints
> __asm__ volatile(".8byte %0\n\t" : : "i" ("message %s\n"));
> ^~~~~~~
> temp.c:4:2: error: impossible constraint in asm
>
> I'd use the "S" constraint.
Thanks that worked.
>
>> I am unable to code something similar manually using inline asm because
>> the string is a format string containing % characters, which inline asm
>> will of course try to interpret. (Does gcc provide anything to escape %
>> chars in a literal string?)
>
> "%%"
>
The problem is that I have literal printf format strings in a multiplatform code base. I need something like a gcc builtin to do the % doubling.
#define X(fmt) asm ("lines " __builtin_escape(fmt) " more lines")
Joe Buehler
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: aph@redhat.com
2020-09-02 18:25 ` aph@redhat.com Joe Buehler
@ 2020-09-03 10:18 ` Andrew Haley
0 siblings, 0 replies; 7+ messages in thread
From: Andrew Haley @ 2020-09-03 10:18 UTC (permalink / raw)
To: Joe Buehler; +Cc: gcc-help
On 02/09/2020 19:25, Joe Buehler wrote:
> Andrew Haley wrote:
>> On 27/08/2020 22:23, Joe Buehler via Gcc-help wrote:
>>
>> temp.c: In function main :
>> temp.c:4:2: warning: asm operand 0 probably doesn t match constraints
>> __asm__ volatile(".8byte %0\n\t" : : "i" ("message %s\n"));
>> ^~~~~~~
>> temp.c:4:2: error: impossible constraint in asm
>>
>> I'd use the "S" constraint.
>
> Thanks that worked.
>
>>> I am unable to code something similar manually using inline asm because
>>> the string is a format string containing % characters, which inline asm
>>> will of course try to interpret. (Does gcc provide anything to escape %
>>> chars in a literal string?)
>>
>> "%%"
>
> The problem is that I have literal printf format strings in a
> multiplatform code base. I need something like a gcc builtin to do
> the % doubling.
>
> #define X(fmt) asm ("lines " __builtin_escape(fmt) " more lines")
I'm not sure I really understand the problem. You only need the "%%"
if the "%" characters are in the actual asm string, not the parameter
passed, which can be any string. If you're assuming that it's possible
to create inline asm code portable across non-GCC compilers, then that
hasn't ever been so.
Having said that, I'm fairly sure that __builtin_escape() could be
written in C++. If you were feeling brave!
--
Andrew Haley (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2020-09-03 10:18 UTC | newest]
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2020-08-27 21:23 aarch64 inline asm / -fPIC problem Joe Buehler
2020-08-28 13:45 ` Joe Buehler
2020-08-28 15:17 ` Joe Buehler
2020-08-29 15:45 ` Andrew Haley
2020-09-02 18:25 ` aph@redhat.com Joe Buehler
2020-09-03 10:18 ` aph@redhat.com Andrew Haley
2020-09-02 18:26 ` aarch64 inline asm / -fPIC problem Joe Buehler
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