[llvm-dev] An error of asm goto occured while compiling Linux kernel 5.3

[Will Lester via llvm-dev]

On Fri, Sep 27, 2019 at 4:02 AM Tim Northover <t.p.northover at gmail.com> wrote:
>
> Hi Will,
>
> I'm adding cfe-dev since this potentially covers both areas.
>
> On Thu, 26 Sep 2019 at 15:45, Will Lester via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > I encountered an error while compiling Linux kernel 5.3 to IR.
> > My LLVM version is 9.0.0 release.
>
> The error message you quote can only be emitted after LLVM has started
> turning IR into machine code. What's the actual Clang command that
> produces this error?
>

I have checked the building process and find the error actually happened when
building a .o file, which is  fs/nfs/flexfilelayout/flexfilelayout.o.

The Clang command is:

clang -Wp,-MD,fs/nfs/flexfilelayout/.flexfilelayout.o.d  -nostdinc
-isystem /usr/local/lib/clang/9.0.0/include -I./arch/x86/include
-I./arch/x86/include/generated  -I./include -I./arch/x86/include/uapi
-I./arch/x86/include/generated/uapi -I./include/uapi -I./include/generated/uapi
-include ./include/linux/kconfig.h -include ./include/linux/compiler_types.h
-D__KERNEL__ -Qunused-arguments -Wall -Wundef -Werror=strict-prototypes
-Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE
-Werror=implicit-function-declaration -Werror=implicit-int -Wno-format-security
-std=gnu89 -no-integrated-as -Werror=unknown-warning-option -mno-sse
-mno-mmx -mno-sse2 -mno-3dnow -mno-avx -m64 -mno-80387 -mstack-alignment=8
-mtune=generic -mno-red-zone -mcmodel=kernel -DCONFIG_X86_X32_ABI
-DCONFIG_AS_CFI=1 -DCONFIG_AS_CFI_SIGNAL_FRAME=1 -DCONFIG_AS_CFI_SECTIONS=1
-DCONFIG_AS_SSSE3=1 -DCONFIG_AS_AVX=1 -DCONFIG_AS_AVX2=1
-DCONFIG_AS_AVX512=1 -DCONFIG_AS_SHA1_NI=1 -DCONFIG_AS_SHA256_NI=1
-Wno-sign-compare -fno-asynchronous-unwind-tables -mretpoline-external-thunk
-fno-delete-null-pointer-checks -Wno-address-of-packed-member -O0
-Wframe-larger-than=2048 -fstack-protector-strong -Wno-format-invalid-specifier
-Wno-gnu -Wno-tautological-compare -mno-global-merge -Wno-unused-const-variable
-fomit-frame-pointer -ftrivial-auto-var-init=pattern -g
-Wdeclaration-after-statement
-Wimplicit-fallthrough -Wvla -Wno-pointer-sign -fno-strict-overflow
-fno-merge-all-constants
-fno-stack-check -Werror=date-time -Werror=incompatible-pointer-types
-fcf-protection=none -Wno-initializer-overrides -Wno-format -Wno-sign-compare
-Wno-format-zero-length   -DMODULE  -DKBUILD_BASENAME='"flexfilelayout"'
-DKBUILD_MODNAME='"nfs_layout_flexfiles"' -c -o
fs/nfs/flexfilelayout/flexfilelayout.o fs/nfs/flexfilelayout/flexfilelayout.c

> > This error said "invalid operand for inline asm constraint 'i'" in
> > arch/x86/include/asm/jump_table.h.
>
> This is a pretty fragile use of that constraint, since it's declaring
> that something must be a constant when that can only happen via
> optimizations. I'm not convinced that's what's going on here though.
> Kernels aren't usually compiled at -O0 and I think I trust the Linux
> developers to make sure users are passing an obvious constant.
>

I am doing an analysis of kernel, therefore I use -O0 to keep details of
source code.

> > The source code is
> > static __always_inline bool arch_static_branch(struct static_key *key,
> > bool branch)
> > {
> > asm_volatile_goto("1:"
> > ".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
> > ".pushsection __jump_table,  \"aw\" \n\t"
> > _ASM_ALIGN "\n\t"
> > ".long 1b - ., %l[l_yes] - . \n\t"
> > _ASM_PTR "%c0 + %c1 - .\n\t"
> > ".popsection \n\t"
> > : :  "i" (key), "i" (branch) : : l_yes);
> >
> > return false;
> > l_yes:
> > return true;
> > }
> >
> > The error pointed to asm_volatile_goto("1:"
> > I'm not sure whether this error is related to asm goto support.