linux-kernel - Re: [PATCH 01/13] objtool: Rewrite hashtable sizing

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Date:   Wed, 12 May 2021 12:41:58 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, jpoimboe@...hat.com, jbaron@...mai.com,
        rostedt@...dmis.org, ardb@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/13] objtool: Rewrite hashtable sizing

On Thu, May 06, 2021 at 09:33:53PM +0200, Peter Zijlstra wrote:
> @@ -343,6 +360,10 @@ static int read_symbols(struct elf *elf)
>  
>  	symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
>  
> +	if (!elf_alloc_hash(symbol, symbols_nr) ||
> +	    !elf_alloc_hash(symbol_name, symbols_nr))
> +		return -1;
> +
>  	for (i = 0; i < symbols_nr; i++) {
>  		sym = malloc(sizeof(*sym));
>  		if (!sym) {

Ingo ran into the empty file without .symtab case with as-2.36.1, which
then means we don't even allocate the symbol hashes which then explodes
later.

The below seems to fix things.

---
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 6942357cd4a2..60bef847ee85 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -340,25 +340,19 @@ static int read_symbols(struct elf *elf)
 {
 	struct section *symtab, *symtab_shndx, *sec;
 	struct symbol *sym, *pfunc;
-	int symbols_nr, i;
+	int i, symbols_nr = 0;
 	char *coldstr;
 	Elf_Data *shndx_data = NULL;
 	Elf32_Word shndx;
 
 	symtab = find_section_by_name(elf, ".symtab");
-	if (!symtab) {
-		/*
-		 * A missing symbol table is actually possible if it's an empty
-		 * .o file.  This can happen for thunk_64.o.
-		 */
-		return 0;
-	}
-
-	symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
-	if (symtab_shndx)
-		shndx_data = symtab_shndx->data;
+	if (symtab) {
+		symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
+		if (symtab_shndx)
+			shndx_data = symtab_shndx->data;
 
-	symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
+		symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
+	}
 
 	if (!elf_alloc_hash(symbol, symbols_nr) ||
 	    !elf_alloc_hash(symbol_name, symbols_nr))