Re: [PATCH] recordmcount: avoid using ABS symbol as reference

On Mon, 7 Jun 2021 13:44:21 +0200
Peter Zijlstra [off-list ref] wrote:

quoted

There's an extended section header index section for just that. And
recordmcount actually seems to use that as well.

I can't seem to find enough of the thread to figure out what the actual
problem is though. The lore archive doesn't have anything prior to this
message.

One should only use st_shndx when >SHN_UDEF and <SHN_LORESERVE. When
SHN_XINDEX, then use .symtab_shndx.

Apparently you've found a case where neither is true? In that case
objtool seems to use shndx 0. A matching recordmcount patch would be
something like this.

Hi Peter,

Should I resend the below patch as v2?

Mark-PK,

Does the below patch fix it for you too (if you backport it to your
kernel). I much rather have recordmcount match objtool, as one day the
two will hopefully merge to one executable.

-- Steve

Yes, this patch fix it.

quoted

diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
index f9b19524da11..d99cc0aed6fe 100644
--- a/scripts/recordmcount.h
+++ b/scripts/recordmcount.h

@@ -194,13 +194,18 @@ static unsigned int get_symindex(Elf_Sym const *sym, Elf32_Word const *symtab,
 	unsigned long offset;
 	int index;
 
-	if (sym->st_shndx != SHN_XINDEX)
+	if (sym->st_shndx > SHN_UDEF &&
+	    sym->st_shndx < SHN_LORESERVE)
 		return w2(sym->st_shndx);
 
-	offset = (unsigned long)sym - (unsigned long)symtab;
-	index = offset / sizeof(*sym);
+	if (sym->st_shndx == SHN_XINDEX) {
+		offset = (unsigned long)sym - (unsigned long)symtab;
+		index = offset / sizeof(*sym);
 
-	return w(symtab_shndx[index]);
+		return w(symtab_shndx[index]);
+	}
+
+	return 0;
 }
 
 static unsigned int get_shnum(Elf_Ehdr const *ehdr, Elf_Shdr const *shdr0)