On Sat, Jun 12, 2021 at 3:47 PM Bill Wendling [off-list ref] wrote:

On Sat, Jun 12, 2021 at 1:56 PM Bill Wendling [off-list ref] wrote:

quoted

On Sat, Jun 12, 2021 at 1:25 PM Peter Zijlstra [off-list ref] wrote:

quoted

On Sat, Jun 12, 2021 at 12:10:03PM -0700, Bill Wendling wrote:
Yes it is, but is that sufficient in this case? It very much isn't for
KASAN, UBSAN, and a whole host of other instrumentation crud. They all
needed their own 'bugger-off' attributes.

Now, for the "nointr" issue. I'll see if we need an additional change for that.

The GCOV implementation disables profiling in those directories where
instrumentation would fail. We do the same. Both clang and gcc seem to
treat the no_instrument_function attribute similarly.

An example:

$ cat n.c
int g(int);

int __attribute__((__no_instrument_function__))
__attribute__((no_instrument_function))
no_instr(int a) {
  int sum = 0;
  for (int i = 0; i < a; i++)
    sum += g(i);
  return sum;
}

int instr(int a) {
  int sum = 0;
  for (int i = 0; i < a; i++)
    sum += g(i);
  return sum;
}

$ gcc -S -o - n.c -fprofile-arcs -ftest-coverage -O2
        .globl  no_instr
        .type   no_instr, @function
no_instr:
.LFB0:
 ...
        addq    $1, __gcov0.no_instr(%rip)
        pushq   %rbp
 ...
.L3:
 ...
        addq    $1, 8+__gcov0.no_instr(%rip)
 ...
        addq    $1, 16+__gcov0.no_instr(%rip)
 ...
        addq    $1, 16+__gcov0.no_instr(%rip)
 ...
        ret
        .globl  instr
        .type   instr, @function
instr:
.LFB1:
 ...
        addq    $1, __gcov0.instr(%rip)
 ...
        addq    $1, 8+__gcov0.instr(%rip)
 ...
        addq    $1, 16+__gcov0.instr(%rip)
 ...
        addq    $1, 16+__gcov0.instr(%rip)
 ...
        ret

$ clang -S -o - n.c -fprofile-generate -O2
        .globl  no_instr                        # -- Begin function no_instr
        .p2align        4, 0x90
        .type   no_instr,@function
no_instr:                               # @no_instr
 ...
        addq    $1, .L__profc_no_instr+8(%rip)
 ...
        movq    .L__profc_no_instr(%rip), %rax
 ...
        movq    %rax, .L__profc_no_instr(%rip)
 ...
        retq
        .globl  instr                           # -- Begin function instr
        .p2align        4, 0x90
        .type   instr,@function
instr:                                  # @instr
 ...
        addq    $1, .L__profc_instr+8(%rip)
 ...
        movq    .L__profc_instr(%rip), %rax
 ...
        movq    %rax, .L__profc_instr(%rip)
 ...
        retq
.Lfunc_end1: