[llvm-bugs] [Bug 26477] New: interrupt handler calls functions with misaligned stack

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=26477

            Bug ID: 26477
           Summary: interrupt handler calls functions with misaligned
                    stack
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedb...@nondot.org
          Reporter: hjl.to...@gmail.com
                CC: amjad.ab...@intel.com, david.l.kreit...@intel.com,
                    kevin.b.sm...@intel.com, llvm-bugs@lists.llvm.org
    Classification: Unclassified

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]$

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