[PATCH] riscv: tracing: Fix __write_overflow_field in ftrace_partial_regs()

[Charlie Jenkins]

On Tue, Feb 25, 2025 at 09:36:04AM +0100, Alexandre Ghiti wrote:
> Hi Charlie,
> 
> On 25/02/2025 03:42, Charlie Jenkins wrote:
> > The size of &regs->a0 is unknown, causing the error:
> > 
> > ../include/linux/fortify-string.h:571:25: warning: call to
> > '__write_overflow_field' declared with attribute warning: detected write
> > beyond size of field (1st parameter); maybe use struct_group()?
> > [-Wattribute-warning]
> 
> 
> I can't reproduce this warning with gcc and llvm, even when setting by hand
> -Wattribute-warning when compiling bpf_trace.c (which is the user of
> ftrace_partial_regs()).
> 
> Which toolchain did you use?

You need to have the configs:
CONFIG_BPF_SYSCALL=y
CONFIG_FORTIFY_SOURCE=y
CONFIG_FUNCTION_TRACER=y
CONFIG_FPROBE=y
CONFIG_DYNAMIC_FTRACE=y

I used gcc 14.2.0

- Charlie

> 
> Thanks,
> 
> Alex
> 
> 
> > 
> > Fix this by wrapping the required registers in pt_regs with
> > struct_group() and reference the group when doing the offending
> > memcpy().
> > 
> > Signed-off-by: Charlie Jenkins <charlie at rivosinc.com>
> > ---
> >   arch/riscv/include/asm/ftrace.h |  2 +-
> >   arch/riscv/include/asm/ptrace.h | 18 ++++++++++--------
> >   2 files changed, 11 insertions(+), 9 deletions(-)
> > 
> > diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> > index c4721ce44ca474654b37b3d51bc0a63d46bc1eff..ec6db1162021fbf4fa48fc87e7984266040aa7d9 100644
> > --- a/arch/riscv/include/asm/ftrace.h
> > +++ b/arch/riscv/include/asm/ftrace.h
> > @@ -207,7 +207,7 @@ ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs)
> >   {
> >   	struct __arch_ftrace_regs *afregs = arch_ftrace_regs(fregs);
> > -	memcpy(&regs->a0, afregs->args, sizeof(afregs->args));
> > +	memcpy(&regs->a_regs, afregs->args, sizeof(afregs->args));
> >   	regs->epc = afregs->epc;
> >   	regs->ra = afregs->ra;
> >   	regs->sp = afregs->sp;
> > diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
> > index b5b0adcc85c18e15c156de11172a5d7f03ada037..2910231977cb71dac3cc42f2dc32590284204057 100644
> > --- a/arch/riscv/include/asm/ptrace.h
> > +++ b/arch/riscv/include/asm/ptrace.h
> > @@ -23,14 +23,16 @@ struct pt_regs {
> >   	unsigned long t2;
> >   	unsigned long s0;
> >   	unsigned long s1;
> > -	unsigned long a0;
> > -	unsigned long a1;
> > -	unsigned long a2;
> > -	unsigned long a3;
> > -	unsigned long a4;
> > -	unsigned long a5;
> > -	unsigned long a6;
> > -	unsigned long a7;
> > +	struct_group(a_regs,
> > +		unsigned long a0;
> > +		unsigned long a1;
> > +		unsigned long a2;
> > +		unsigned long a3;
> > +		unsigned long a4;
> > +		unsigned long a5;
> > +		unsigned long a6;
> > +		unsigned long a7;
> > +	);
> >   	unsigned long s2;
> >   	unsigned long s3;
> >   	unsigned long s4;
> > 
> > ---
> > base-commit: d082ecbc71e9e0bf49883ee4afd435a77a5101b6
> > change-id: 20250224-fix_ftrace_partial_regs-eddaf4a7e5ed