Commit Graph

8 Commits

Author SHA1 Message Date
Adrian Prantl 083e6a5b5c Don't emit CFI instructions at the end of a function
When functions are terminated by unreachable instructions, the last
instruction might trigger a CFI instruction to be generated. However,
emitting it would be be illegal since the function (and thus the FDE
the CFI is in) has already ended with the previous instruction.

Darwin's dwarfdump --verify --eh-frame complains about this and the
specification supports this.
Relevant bits from the DWARF 5 standard (6.4 Call Frame Information):

"[The] address_range [field in an FDE]: The number of bytes of
 program instructions described by this entry."

"Row creation instructions: [...]
 The new location value is always greater than the current one."
The first quotation implies that a CFI cannot describe a target
address outside of the enclosing FDE's range.

rdar://problem/26244988

Differential Revision: https://reviews.llvm.org/D32246

llvm-svn: 301219
2017-04-24 18:45:59 +00:00
Rafael Espindola 310e4b592f Use the vanilla func_end symbol for .size.
No need to create yet another temp symbol.

llvm-svn: 231198
2015-03-04 01:35:23 +00:00
Rafael Espindola 6865d6f08a Fix a lot of confusion around inserting nops on empty functions.
On MachO, and MachO only, we cannot have a truly empty function since that
breaks the linker logic for atomizing the section.

When we are emitting a frame pointer, the presence of an unreachable will
create a cfi instruction pointing past the last instruction. This is perfectly
fine. The FDE information encodes the pc range it applies to. If some tool
cannot handle this, we should explicitly say which bug we are working around
and only work around it when it is actually relevant (not for ELF for example).

Given the unreachable we could omit the .cfi_def_cfa_register, but then
again, we could also omit the entire function prologue if we wanted to.

llvm-svn: 217801
2014-09-15 18:32:58 +00:00
Rafael Espindola f28213ca01 Don't print an unused label before .cfi_endproc.
llvm-svn: 147763
2012-01-09 00:17:29 +00:00
Rafael Espindola 382412032c Don't print a label before .cfi_startproc when we don't need to. This makes
the produce assembly when using CFI just a bit more readable.

llvm-svn: 147743
2012-01-07 22:42:19 +00:00
Rafael Espindola 08600bcf65 Use the dwarf->llvm mapping to print register names in the cfi
directives.

Fixes PR9826.

llvm-svn: 132317
2011-05-30 20:20:15 +00:00
Rafael Espindola a4982bddf3 Don't produce a __debug_frame.
I tested both gdb on a bootstrapped clang and and the gdb testsuite on OS X (snow leopard)
and both are happy using __eh_frame.

llvm-svn: 130937
2011-05-05 18:43:39 +00:00
Bill Wendling bf8370ff36 Consider this function:
void foo() { __builtin_unreachable(); }

It will output the following on Darwin X86:

_func1:
Leh_func_begin0:
        pushq %rbp
Ltmp0:
        movq %rsp, %rbp
Ltmp1:
Leh_func_end0:

This prolog adds a new Call Frame Information (CFI) row to the FDE with an
address that is not within the address range of the code it describes -- part is
equal to the end of the function -- and therefore results in an invalid EH
frame. If we emit a nop in this situation, then the CFI row is now within the
address range.

llvm-svn: 108568
2010-07-16 22:51:10 +00:00