[PATCH] symbols: explicitly specify source file name for symtab

[Jan Beulich <jbeulich@xxxxxxxx>]

If there are any local symbols in an object file, GNU ld will create an
STT_FILE symbol derived from the object file name if there is none in the
incoming symbol table. The object file name, however, varies between
linking passes. As a result, symbol name compression can yield different
results if any of those local symbols need retaining (Arm [and RISC-V]
mapping symbols are omitted, for example). If that difference in
compression would yield a difference in the sizes of symbol_names[] or
symbols_token_table[], the compare-symbol-tables sanity check will fail.

Fixes: d37d63d4b548 ("symbols: prefix static symbols with their source file 
names")
Reported-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
The observed problem was with a stub generated as Arm64 erratum 843419
workaround. Such stubs' symbols (imo wrongly) are associated with the last
input object, rather than the input object they belong to. Also for other
kinds of stubs, afaict. See
https://sourceware.org/bugzilla/show_bug.cgi?id=34140.

As per the above, having a Fixes: tag here is questionable.

--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -200,7 +200,8 @@ $(TARGET).efi: $(objtree)/prelink.o $(no
 ifeq ($(CONFIG_DEBUG_INFO),y)
        $(if $(filter --strip-debug,$(EFI_LDFLAGS)),echo,:) "Will strip debug 
info from $(@F)"
 endif
-       $(objtree)/tools/symbols $(all_symbols) --empty > $(dot-target).0s.S
+       $(objtree)/tools/symbols $(all_symbols) --source-name=$(@F).S --empty \
+               > $(dot-target).0s.S
        $(MAKE) $(build)=$(@D) .$(@F).0s.o
        $(foreach base, $(VIRT_BASE) $(ALT_BASE), \
                  $(LD) $(call EFI_LDFLAGS,$(base)) -T $(obj)/efi.lds $< 
$(relocs-dummy) \
@@ -210,6 +211,7 @@ endif
                > $(dot-target).1r.S
        $(NM) -pa --format=sysv $(dot-target).$(VIRT_BASE).0 \
                | $(objtree)/tools/symbols $(all_symbols) --sysv --sort \
+                  --source-name=$(@F).S \
                > $(dot-target).1s.S
        $(MAKE) $(build)=$(@D) .$(@F).1r.o .$(@F).1s.o
        $(foreach base, $(VIRT_BASE) $(ALT_BASE), \
@@ -220,6 +222,7 @@ endif
                > $(dot-target).2r.S
        $(NM) -pa --format=sysv $(dot-target).$(VIRT_BASE).1 \
                | $(objtree)/tools/symbols $(all_symbols) --sysv --sort \
+                  --source-name=$(@F).S \
                > $(dot-target).2s.S
        $(MAKE) $(build)=$(@D) .$(@F).2r.o .$(@F).2s.o
        $(call compare-symbol-tables, $(dot-target).1r.o, $(dot-target).2r.o)
--- a/xen/tools/symbols.c
+++ b/xen/tools/symbols.c
@@ -66,6 +66,7 @@ int token_profit[0x10000];
 unsigned char best_table[256][2];
 unsigned char best_table_len[256];
 
+static const char *srcname = "xen-syms.S";
 
 static void usage(void)
 {
@@ -356,6 +357,7 @@ static void write_src(void)
        printf("#define ALGN 4\n");
        printf("#endif\n");
 
+       printf("\t.file \"%s\"\n", srcname);
        printf("\t.section .rodata, \"a\"\n");
 
        printf("#ifndef SYMBOLS_ORIGIN\n");
@@ -679,6 +681,8 @@ int main(int argc, char **argv)
                                unsorted = true;
                        else if (strcmp(argv[i], "--sort-by-name") == 0)
                                sort_by_name = 1;
+                       else if (strncmp(argv[i], "--source-name=", 14) == 0)
+                               srcname = argv[i] + 14;
                        else if (strcmp(argv[i], "--warn-dup") == 0)
                                warn_dup = true;
                        else if (strcmp(argv[i], "--error-dup") == 0)