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From: "andrew.cooper3 at citrix dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/102953] Improvements to CET-IBT and ENDBR generation
Date: Wed, 27 Oct 2021 18:50:42 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102953

--- Comment #7 from Andrew Cooper <andrew.cooper3 at citrix dot com> ---
Thankyou.  I've tried these two patches and they do appear to be behaving as
intended.

I've put together a slightly extended version of the original test.  Compile
with gcc -Wall -fno-pic -Os -fcf-protection=3Dbranch -mmanual-endbr
-fcf-check-attribute=3Dno

static void __attribute__((noinline)) a(void)
{
    asm volatile ("sti":::"memory");
}

void __attribute__((nocf_check, noinline)) b(void)
{
    asm volatile ("std":::"memory");
}

void __attribute__((cf_check, noinline)) c(void)
{
    asm volatile ("cmc":::"memory");
}

void (*ptr_a)(void) =3D a; // Now raises a diagnostic
void (*ptr_b)(void) =3D b; // Did diagnose previously, still does
void (*ptr_c)(void) =3D c;

int test(void)
{
    ptr_a();
    ptr_b();
    ptr_c();

    a();
    b();
    c(); // When fully linked, does skip c's ENDBR64 instruction

    return 0;
}

int main(void)
{
    return 0;
}

I'll try applying this to a bigger codebase now.=