4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Josh Poimboeuf jpoimboe@redhat.com
[ Upstream commit 08b393d01c88aff27347ed2b1b354eb4db2f1532 ]
Since the following commit:
cd77849a69cf ("objtool: Fix GCC 8 cold subfunction detection for aliased functions")
... if the kernel is built with EXTRA_CFLAGS='-fno-reorder-functions', objtool can get stuck in an infinite loop.
That flag causes the new GCC 8 cold subfunctions to be placed in .text instead of .text.unlikely. But it also has an unfortunate quirk: in the symbol table, the subfunction (e.g., nmi_panic.cold.7) is nested inside the parent (nmi_panic).
That function overlap confuses objtool, and causes it to get into an infinite loop in next_insn_same_func(). Here's Allan's description of the loop:
"Objtool iterates through the instructions in nmi_panic using next_insn_same_func. Once it reaches the end of nmi_panic at 0x534 it jumps to 0x528 as that's the start of nmi_panic.cold.7. However, since the instructions starting at 0x528 are still associated with nmi_panic objtool will get stuck in a loop, continually jumping back to 0x528 after reaching 0x534."
Fix it by shortening the length of the parent function so that the functions no longer overlap.
Reported-and-analyzed-by: Allan Xavier allan.x.xavier@oracle.com Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Cc: Allan Xavier allan.x.xavier@oracle.com Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: Brian Gerst brgerst@gmail.com Cc: Denys Vlasenko dvlasenk@redhat.com Cc: H. Peter Anvin hpa@zytor.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Link: http://lkml.kernel.org/r/9e704c52bee651129b036be14feda317ae5606ae.1530136978... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- tools/objtool/elf.c | 37 ++++++++++++++++++++++++++----------- 1 file changed, 26 insertions(+), 11 deletions(-)
--- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -302,19 +302,34 @@ static int read_symbols(struct elf *elf) continue; sym->pfunc = sym->cfunc = sym; coldstr = strstr(sym->name, ".cold."); - if (coldstr) { - coldstr[0] = '\0'; - pfunc = find_symbol_by_name(elf, sym->name); - coldstr[0] = '.'; + if (!coldstr) + continue; + + coldstr[0] = '\0'; + pfunc = find_symbol_by_name(elf, sym->name); + coldstr[0] = '.'; + + if (!pfunc) { + WARN("%s(): can't find parent function", + sym->name); + goto err; + }
- if (!pfunc) { - WARN("%s(): can't find parent function", - sym->name); - goto err; - } + sym->pfunc = pfunc; + pfunc->cfunc = sym;
- sym->pfunc = pfunc; - pfunc->cfunc = sym; + /* + * Unfortunately, -fnoreorder-functions puts the child + * inside the parent. Remove the overlap so we can + * have sane assumptions. + * + * Note that pfunc->len now no longer matches + * pfunc->sym.st_size. + */ + if (sym->sec == pfunc->sec && + sym->offset >= pfunc->offset && + sym->offset + sym->len == pfunc->offset + pfunc->len) { + pfunc->len -= sym->len; } } }