linux-kernel - Re: [PATCH v6 02/18] gendwarfksyms: Add address matching

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Message-ID: <de6b416c-b96a-43aa-ad72-ea365ffbe785@suse.com>
Date: Mon, 2 Dec 2024 17:08:49 +0100
From: Petr Pavlu <petr.pavlu@...e.com>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
 Luis Chamberlain <mcgrof@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Matthew Maurer <mmaurer@...gle.com>, Alex Gaynor <alex.gaynor@...il.com>,
 Gary Guo <gary@...yguo.net>, Petr Pavlu <petr.pavlu@...e.com>,
 Daniel Gomez <da.gomez@...sung.com>, Neal Gompa <neal@...pa.dev>,
 Hector Martin <marcan@...can.st>, Janne Grunau <j@...nau.net>,
 Miroslav Benes <mbenes@...e.cz>, Asahi Linux <asahi@...ts.linux.dev>,
 Sedat Dilek <sedat.dilek@...il.com>, linux-kbuild@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v6 02/18] gendwarfksyms: Add address matching

On 11/21/24 21:42, Sami Tolvanen wrote:
> The compiler may choose not to emit type information in DWARF for all
> aliases, but it's possible for each alias to be exported separately.
> To ensure we find type information for the aliases as well, read
> {section, address} tuples from the symbol table and match symbols also
> by address.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> ---
[...]
> @@ -82,6 +118,130 @@ struct symbol *symbol_get(const char *name)
>  	return sym;
>  }
>  
> +typedef void (*elf_symbol_callback_t)(const char *name, GElf_Sym *sym,
> +				      Elf32_Word xndx, void *arg);
> +
> +static void elf_for_each_global(int fd, elf_symbol_callback_t func, void *arg)
> +{
> +	size_t sym_size;
> +	GElf_Shdr shdr_mem;
> +	GElf_Shdr *shdr;
> +	Elf_Data *xndx_data = NULL;
> +	Elf_Scn *scn;
> +	Elf *elf;
> +
> +	if (elf_version(EV_CURRENT) != EV_CURRENT)
> +		error("elf_version failed: %s", elf_errmsg(-1));
> +
> +	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
> +	if (!elf)
> +		error("elf_begin failed: %s", elf_errmsg(-1));
> +
> +	scn = elf_nextscn(elf, NULL);
> +
> +	while (scn) {
> +		shdr = gelf_getshdr(scn, &shdr_mem);
> +		if (!shdr)
> +			error("gelf_getshdr failed: %s", elf_errmsg(-1));
> +
> +		if (shdr->sh_type == SHT_SYMTAB_SHNDX) {
> +			xndx_data = elf_getdata(scn, NULL);
> +			if (!xndx_data)
> +				error("elf_getdata failed: %s", elf_errmsg(-1));
> +			break;
> +		}
> +
> +		scn = elf_nextscn(elf, scn);
> +	}
> +
> +	sym_size = gelf_fsize(elf, ELF_T_SYM, 1, EV_CURRENT);
> +	scn = elf_nextscn(elf, NULL);
> +
> +	while (scn) {
> +		shdr = gelf_getshdr(scn, &shdr_mem);
> +		if (!shdr)
> +			error("gelf_getshdr failed: %s", elf_errmsg(-1));
> +
> +		if (shdr->sh_type == SHT_SYMTAB) {
> +			unsigned int nsyms;
> +			unsigned int n;
> +			Elf_Data *data = elf_getdata(scn, NULL);
> +
> +			if (!data)
> +				error("elf_getdata failed: %s", elf_errmsg(-1));
> +
> +			if (shdr->sh_entsize != sym_size)
> +				error("expected sh_entsize (%lu) to be %zu",
> +				      shdr->sh_entsize, sym_size);
> +
> +			nsyms = shdr->sh_size / shdr->sh_entsize;
> +
> +			for (n = 1; n < nsyms; ++n) {
> +				const char *name = NULL;
> +				Elf32_Word xndx = 0;
> +				GElf_Sym sym_mem;
> +				GElf_Sym *sym;
> +
> +				sym = gelf_getsymshndx(data, xndx_data, n,
> +						       &sym_mem, &xndx);
> +
> +				if (!sym ||
> +				    GELF_ST_BIND(sym->st_info) == STB_LOCAL)
> +					continue;

Doesn't NULL returned by gelf_getsymshndx() indicate an error? If yes
then I think it should be reported instead of silently skipping the
symbol.

With this addressed, feel free to add:
Reviewed-by: Petr Pavlu <petr.pavlu@...e.com>

-- 
Thanks,
Petr