From: YASUOKA Masahiko <yasuoka@openbsd.org>
Subject: Re: lldb: fails to read a process core file (regression)
To: asou@openbsd.org
Cc: naito.yuichiro@gmail.com, tech@openbsd.org
Date: Wed, 31 Jul 2024 17:29:56 +0900

Asou-san,

Can you handle this? 

ok yasuoka

On Wed, 31 Jul 2024 16:38:25 +0900 (JST)
Yuichiro NAITO <naito.yuichiro@gmail.com> wrote:
> I received a mail personally that reports lldb fails to read a process core
> file. It's a regression of my kernel core file support patch. My apologies.
> 
> The ProcessOpenBSDKernel class opens a core file via kvm_open(3).
> The kvm_open(3) succeeds in opening a core file even if it is a process core.
> So the OpenBSDKernel plugin is used for a process core file but can't analyze
> it.
> 
> If a process core file is passed to the ProcessOpenBSDKernel class, its
> instantiation should fail. A process core file is an ELF binary. I add
> the check logic to see whether an ELF binary or not and make it fail
> instantiation in case of an ELF binary.
> 
> OK?
> 
> diff --git a/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/ProcessOpenBSDKernel.cpp b/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/ProcessOpenBSDKernel.cpp
> index 300a35d4051..8016399586f 100644
> --- a/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/ProcessOpenBSDKernel.cpp
> +++ b/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/ProcessOpenBSDKernel.cpp
> @@ -19,6 +19,7 @@
>  #define _KERNEL
>  #include <machine/cpu.h>
>  #include <sys/proc.h>
> +#include <sys/exec_elf.h>
>  #undef _KERNEL
>  #endif
>  
> @@ -60,6 +61,14 @@ lldb::ProcessSP ProcessOpenBSDKernel::CreateInstance(lldb::TargetSP target_sp,
>    ModuleSP executable = target_sp->GetExecutableModule();
>    if (crash_file && !can_connect && executable) {
>  #if defined(__OpenBSD__)
> +    char buf[4];
> +    FILE *fp = fopen(crash_file->GetPath().c_str(), "r");
> +    if (fp == NULL)
> +      return nullptr;
> +    size_t r = fread(buf, 1, sizeof(buf), fp);
> +    fclose(fp);
> +    if (r != sizeof(buf) || memcmp(buf, ELFMAG, sizeof(buf)) == 0)
> +      return nullptr;
>      kvm_t *kvm =
>          kvm_open(executable->GetFileSpec().GetPath().c_str(),
>  		 crash_file->GetPath().c_str(), nullptr, O_RDONLY, nullptr);
> 
> -- 
> Yuichiro NAITO (naito.yuichiro@gmail.com)
> 
>