[patch 2.6.20-rc4-git] remove modpost false warnings on ARM

David Brownell
2007-01-12T16:31:53Z

builds, which it's been doing simce 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 "$d" symbol is generated by tools conformant with ARM ABI specs; in
this case, it's a relocation in the start of a "<name>_driver" struct.
The erroneous warnings appear to be issued because "modpost" whitelists
references from "<name>_driver" data into init and exit sections ... but
does NOT whitelist them from "$d" (and can't).

This patch prevents the modpost symbol lookup code from ever returning
those symbols, so it will return a whitelisted symbol instead.

Now to revert various code-bloating "fixes" that got merged because of
this modpost bug....

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

---
Likely this patch can be improved on, but there's another issue.
It seems to me that these modpost checks are wrong:

* Lingering pointers that point into sections modprobe removes are
*always* unsafe ... including probe() methods marked "__init"
on hotpluggable busses. Trivial fix: use __devinit instead;
or maybe platform_driver_probe().
* Lingering pointers that point into sections that aren't removed
are *never* unsafe ... including this remove() method case, since
module unloading is configured and the __exit stuff must stay.

Whitelisting the former means not reporting potential oopsing cases;
dangerous. Whereas even *checking* the latter is a waste of effort.

Index: at91/scripts/mod/modpost.c
===================================================================
--- at91.orig/scripts/mod/modpost.c 2007-01-11 22:51:49.000000000 -0800
+++ at91/scripts/mod/modpost.c 2007-01-12 04:20:00.000000000 -0800
@@ -679,6 +679,26 @@ static Elf_Sym *find_elf_symbol(struct e
}

/*
+ * 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 shrinking __exit and __init sections into __text, bloating
+ * the kernel (which is especially evil on embedded platforms).
+ */
+static 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;
+ if (strcmp(name, "$a") == 0 || strcmp(name, "$d") == 0)
+ return 0;
+ return 1;
+}
+
+/*
* 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
@@ -706,16 +726,15 @@ static void find_symbols_between(struct
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
@@ -725,10 +744,7 @@ static void find_symbols_between(struct