Hi, As I sent already the error message shows the discrepancy starts from include/linux/cache.h, So I added the same #pragma thing around that #include <linux/cache.h> and the compile error is gone. This is only for debugging a boot failure in a qemu machine (which is for a real fpga board), so I can follow the code with gdb. And I needed to analyzing what kernel does until the problem occurs, though it isn't an easy task for me to follow.(but I think it's worth it.) Thanks for the comments. Chan

-----Original Message----- From: jim.cromie@gmail.com <jim.cromie@gmail.com> Sent: Monday, January 24, 2022 1:47 AM To: Chan Kim <ckim@etri.re.kr> Cc: kernelnewbies <kernelnewbies@kernelnewbies.org> Subject: Re: adding GCC optimze O0 to early_fixmap_init causes compiler error (BUILD_BUG failed)

On Sun, Jan 23, 2022 at 4:23 AM Chan Kim <ckim@etri.re.kr> wrote:

...

Hello all,

In linux 5.4.21, when tell the compiler to use no optimzation for function early_fixmap_init as below,

(I need to compile with O0 to follow what’s happening here using gdb.)

#pragma GCC push_options

#pragma GCC optimze ("O0")

void __init early_fixmap_init(void)

{

...

}

#pragma GCC pop_options

I get this compiler error below. (make ARCH=arm64 CROSS_COMPILE=aarch64-none-elf- Image -j24)

CALL scripts/atomic/check-atomics.sh

CALL scripts/checksyscalls.sh

CHK include/generated/compile.h

CC arch/arm64/mm/mmu.o

CC drivers/irqchip/irq-gic-v3.o

In file included from ./include/linux/build_bug.h:5,

from ./arch/arm64/include/asm/sysreg.h:758,

from ./arch/arm64/include/asm/cputype.h:126,

from ./arch/arm64/include/asm/cache.h:8,

from ./include/linux/cache.h:6,

from arch/arm64/mm/mmu.c:9:

./arch/arm64/include/asm/pgalloc.h: In function

'__pgd_populate.constprop':

...

./include/linux/compiler.h:350:38: error: call to '__compiletime_assert_88' declared with attribute error: BUILD_BUG failed

350 | _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)

| ^

./include/linux/compiler.h:331:4: note: in definition of macro

'__compiletime_assert'

...

331 | prefix ## suffix(); \

| ^~~~~~

./include/linux/compiler.h:350:2: note: in expansion of macro

'_compiletime_assert'

...

350 | _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)

| ^~~~~~~~~~~~~~~~~~~

./include/linux/build_bug.h:39:37: note: in expansion of macro

'compiletime_assert'

...

39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)

| ^~~~~~~~~~~~~~~~~~

./include/linux/build_bug.h:59:21: note: in expansion of macro

'BUILD_BUG_ON_MSG'

...

59 | #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")

| ^~~~~~~~~~~~~~~~

./arch/arm64/include/asm/pgalloc.h:88:2: note: in expansion of macro

'BUILD_BUG'

...

88 | BUILD_BUG();

| ^~~~~~~~~

make[2]: *** [scripts/Makefile.build:265: arch/arm64/mm/mmu.o] Error 1

make[1]: *** [scripts/Makefile.build:509: arch/arm64/mm] Error 2

make: *** [Makefile:1652: arch/arm64] Error 2

make: *** Waiting for unfinished jobs....

AR drivers/irqchip/built-in.a

AR drivers/built-in.

What does this mean and what should I do?

it means that some precondition failed, and you reached a known broken setup. Instead of giving you a broken kernel, its told you that you have to fix this 1st.

try making an intermediate output, forex: make init/main.i

that should provide hints as to how you got to the BUILD_BUG

I dont think banging on -O compile options will help, at least not after seeing GregKH opine on it.

...

Thanks!

Chan Kim

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