interrupt handler calls functions with misaligned stack · Issue #26851 · llvm/llvm-project (original) (raw)

Extended Description

Incoming stack of x86 interrupt handler is aligned at 4 bytes (8 bytes for
64-bit). When it calls extern functions, it needs to realign the stack
to 16-byte aligned if it is required:

[hjl@gnu-6 interrupt-1]$ cat xx.i 
extern void bar (void);

extern int i;

void
 __attribute__ ((interrupt))
foo (void *frame)
{
  bar ();
  i = 0;
}
[hjl@gnu-6 interrupt-1]$ /export/build/gnu/gcc-5/build-x86_64-linux/gcc/xgcc -B/export/build/gnu/gcc-5/build-x86_64-linux/gcc/ -O2 xx.i -m32 -mno-sse -S
[hjl@gnu-6 interrupt-1]$  cat xx.s
    .file	"xx.i"
    .section	.text.unlikely,"ax",@progbits
.LCOLDB0:
    .text
.LHOTB0:
    .p2align 4,,15
    .globl	foo
    .type	foo, @function
foo:
.LFB0:
    .cfi_startproc
    pushl	%ebp
    .cfi_def_cfa_offset 8
    .cfi_offset 5, -8
    movl	%esp, %ebp
    .cfi_def_cfa_register 5
    pushl	%ecx
    pushl	%edx
    pushl	%eax
    andl	$-16, %esp  <<<<<<<<<<<< Align stack
    cld
    .cfi_offset 1, -12
    .cfi_offset 2, -16
    .cfi_offset 0, -20
    call	bar
    movl	$0, i
    leal	-12(%ebp), %esp
    popl	%eax
    .cfi_restore 0
    popl	%edx
    .cfi_restore 2
    popl	%ecx
    .cfi_restore 1
    popl	%ebp
    .cfi_restore 5
    .cfi_def_cfa 4, 4
    iret
    .cfi_endproc
.LFE0:
    .size	foo, .-foo
    .section	.text.unlikely
.LCOLDE0:
    .text
.LHOTE0:
    .ident	"GCC: (GNU) 5.3.1 20160201"
    .section	.note.GNU-stack,"",@progbits
[hjl@gnu-6 interrupt-1]$ 

But clang doesn't align stack:

[hjl@gnu-6 interrupt-1]$ /net/gnu-mic-2//export/build/gnu/llvm-clang/build-x86_64-linux/bin/clang -O2 xx.i -m32 -mno-sse -S
[hjl@gnu-6 interrupt-1]$  cat xx.s
    .text
    .file	"xx.i"
    .globl	foo
    .p2align	4, 0x90
    .type	foo,@function
foo:                                    # @foo
# BB#0:
    pushl	%esp
    pushl	%edx
    pushl	%ecx
    pushl	%eax
    subl	$12, %esp
    calll	bar
    movl	$0, i
    addl	$12, %esp
    popl	%eax
    popl	%ecx
    popl	%edx
    popl	%esp
    iretl
.Lfunc_end0:
    .size	foo, .Lfunc_end0-foo


    .ident	"clang version 3.9.0 (http://llvm.org/git/clang.git bf1d31e84aa2722174da56b8aff311ae04f4d9e1) (http://llvm.org/git/llvm.git 6cced9c3cd18f529420a03b100970d97512bb9a4)"
    .section	".note.GNU-stack","",@progbits
[hjl@gnu-6 interrupt-1]$