[PATCH] remove modpost false warnings on ARM

This patch stops "modpost" from issuing erroneous modpost warnings on ARM builds, which it's been doing since since maybe last summer. A canonical example would be driver method table entries: WARNING: <path> - Section mismatch: reference to .exit.text:<name>_remove from .data after '$d' (at offset 0x4) That "$d" symbol is generated by tools conformant with ARM ABI specs; in this case it's a symbol **in the middle of** a "<name>_driver" struct. The erroneous warnings appear to be issued because "modpost" whitelists references from "<name>_driver" data into init and exit sections ... but doesn't know should also include those "$d" mapping symbols, which are not otherwise associated with "<name>_driver" symbols. This patch prevents the modpost symbol lookup code from ever returning those mapping symbols, so it will return a whitelisted symbol instead. Then things work as expected. Now to revert various code-bloating "fixes" that got merged because of this modpost bug.... Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Acked-by: Rusty Russell <rusty@rustcorp.com.au> Cc: Roman Zippel <zippel@linux-m68k.org> Acked-by: Sam Ravnborg <sam@ravnborg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

[PATCH] remove modpost false warnings on ARM
This patch stops "modpost" from issuing erroneous modpost warnings on ARM builds, which it's been doing since since maybe last summer. A canonical example would be driver method table entries: WARNING: <path> - Section mismatch: reference to .exit.text:<name>_remove from .data after '$d' (at offset 0x4) That "$d" symbol is generated by tools conformant with ARM ABI specs; in this case it's a symbol **in the middle of** a "<name>_driver" struct. The erroneous warnings appear to be issued because "modpost" whitelists references from "<name>_driver" data into init and exit sections ... but doesn't know should also include those "$d" mapping symbols, which are not otherwise associated with "<name>_driver" symbols. This patch prevents the modpost symbol lookup code from ever returning those mapping symbols, so it will return a whitelisted symbol instead. Then things work as expected. Now to revert various code-bloating "fixes" that got merged because of this modpost bug.... Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Acked-by: Rusty Russell <rusty@rustcorp.com.au> Cc: Roman Zippel <zippel@linux-m68k.org> Acked-by: Sam Ravnborg <sam@ravnborg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
David Brownell · Linus Torvalds
1 parent 3deac046e2
Showing 1 changed file with 28 additions and 8 deletions Side-by-side Diff
scripts/mod/modpost.c
@@ -686,7 +686,31 @@
 	return NULL;
 }
  
+static inline int is_arm_mapping_symbol(const char *str)
+{
+	return str[0] == '$' && strchr("atd", str[1])
+	       && (str[2] == '\0' || str[2] == '.');
+}
+
 /*
+ * If there's no name there, ignore it; likewise, ignore it if it's
+ * one of the magic symbols emitted used by current ARM tools.
+ *
+ * Otherwise if find_symbols_between() returns those symbols, they'll
+ * fail the whitelist tests and cause lots of false alarms ... fixable
+ * only by merging __exit and __init sections into __text, bloating
+ * the kernel (which is especially evil on embedded platforms).
+ */
+static inline int is_valid_name(struct elf_info *elf, Elf_Sym *sym)
+{
+	const char *name = elf->strtab + sym->st_name;
+
+	if (!name || !strlen(name))
+		return 0;
+	return !is_arm_mapping_symbol(name);
+}
+
+/*
  * Find symbols before or equal addr and after addr - in the section sec.
  * If we find two symbols with equal offset prefer one with a valid name.
  * The ELF format may have a better way to detect what type of symbol
  
@@ -714,16 +738,15 @@
 		symsec = secstrings + elf->sechdrs[sym->st_shndx].sh_name;
 		if (strcmp(symsec, sec) != 0)
 			continue;
+		if (!is_valid_name(elf, sym))
+			continue;
 		if (sym->st_value <= addr) {
 			if ((addr - sym->st_value) < beforediff) {
 				beforediff = addr - sym->st_value;
 				*before = sym;
 			}
 			else if ((addr - sym->st_value) == beforediff) {
-				/* equal offset, valid name? */
-				const char *name = elf->strtab + sym->st_name;
-				if (name && strlen(name))
-					*before = sym;
+				*before = sym;
 			}
 		}
 		else
@@ -733,10 +756,7 @@
 				*after = sym;
 			}
 			else if ((sym->st_value - addr) == afterdiff) {
-				/* equal offset, valid name? */
-				const char *name = elf->strtab + sym->st_name;
-				if (name && strlen(name))
-					*after = sym;
+				*after = sym;
 			}
 		}
 	}
...	...	@@ -686,7 +686,31 @@
686	686	return NULL;
687	687	}
688	688
	689	+static inline int is_arm_mapping_symbol(const char *str)
	690	+{
	691	+ return str[0] == '$' && strchr("atd", str[1])
	692	+ && (str[2] == '\0' \|\| str[2] == '.');
	693	+}
	694	+
689	695	/*
	696	+ * If there's no name there, ignore it; likewise, ignore it if it's
	697	+ * one of the magic symbols emitted used by current ARM tools.
	698	+ *
	699	+ * Otherwise if find_symbols_between() returns those symbols, they'll
	700	+ * fail the whitelist tests and cause lots of false alarms ... fixable
	701	+ * only by merging __exit and __init sections into __text, bloating
	702	+ * the kernel (which is especially evil on embedded platforms).
	703	+ */
	704	+static inline int is_valid_name(struct elf_info elf, Elf_Sym sym)
	705	+{
	706	+ const char *name = elf->strtab + sym->st_name;
	707	+
	708	+ if (!name \|\| !strlen(name))
	709	+ return 0;
	710	+ return !is_arm_mapping_symbol(name);
	711	+}
	712	+
	713	+/*
690	714	* Find symbols before or equal addr and after addr - in the section sec.
691	715	* If we find two symbols with equal offset prefer one with a valid name.
692	716	* The ELF format may have a better way to detect what type of symbol
693	717
...	...	@@ -714,16 +738,15 @@
714	738	symsec = secstrings + elf->sechdrs[sym->st_shndx].sh_name;
715	739	if (strcmp(symsec, sec) != 0)
716	740	continue;
	741	+ if (!is_valid_name(elf, sym))
	742	+ continue;
717	743	if (sym->st_value <= addr) {
718	744	if ((addr - sym->st_value) < beforediff) {
719	745	beforediff = addr - sym->st_value;
720	746	*before = sym;
721	747	}
722	748	else if ((addr - sym->st_value) == beforediff) {
723		- /* equal offset, valid name? */
724		- const char *name = elf->strtab + sym->st_name;
725		- if (name && strlen(name))
726		- *before = sym;
	749	+ *before = sym;
727	750	}
728	751	}
729	752	else
...	...	@@ -733,10 +756,7 @@
733	756	*after = sym;
734	757	}
735	758	else if ((sym->st_value - addr) == afterdiff) {
736		- /* equal offset, valid name? */
737		- const char *name = elf->strtab + sym->st_name;
738		- if (name && strlen(name))
739		- *after = sym;
	759	+ *after = sym;
740	760	}
741	761	}
742	762	}