recordmcount: Correct st_shndx handling

One should only use st_shndx when >SHN_UNDEF and <SHN_LORESERVE. When
SHN_XINDEX, then use .symtab_shndx. Otherwise use 0.

This handles the case: st_shndx >= SHN_LORESERVE && st_shndx != SHN_XINDEX.

Link: https://lore.kernel.org/lkml/[email protected]/
Link: https://lkml.kernel.org/r/[email protected]

Reported-by: Mark-PK Tsai <[email protected]>
Tested-by: Mark-PK Tsai <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
[handle endianness of sym->st_shndx]
Signed-off-by: Mark-PK Tsai <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

Author: Peter Zijlstra

scripts/recordmcount.h

@@ -192,15 +192,20 @@ static unsigned int get_symindex(Elf_Sym const *sym, Elf32_Word const *symtab,
 				 Elf32_Word const *symtab_shndx)
 {
 	unsigned long offset;
+	unsigned short shndx = w2(sym->st_shndx);
 	int index;
 
-	if (sym->st_shndx != SHN_XINDEX)
-		return w2(sym->st_shndx);
+	if (shndx > SHN_UNDEF && shndx < SHN_LORESERVE)
+		return shndx;
 
-	offset = (unsigned long)sym - (unsigned long)symtab;
-	index = offset / sizeof(*sym);
+	if (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)