https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83967
Bug ID: 83967
Summary: LTO removes C functions declared as weak in
assembler(depending on files order in linking)
Product: gcc
Version: 7.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: lto
Assignee: unassigned at gcc dot gnu.org
Reporter: hurwic8 at gmail dot com
CC: marxin at gcc dot gnu.org
Target Milestone: ---
I've observed strange behaviour of the link-time optimization on GCC 7.2.1,
exact version: gcc version 7.2.1 20170904 (release) [ARM/embedded-7-branch
revision 255204] (GNU Tools for Arm Embedded Processors 7-2017-q4-major)
I have project that is compiled for the microcontroller. In startup file, that
is written in assembler, there are weak definitions of the interrupt handlers.
Some of those weak functions are defined in the project C files.
Strange behaviour occurs when I set -flto flag on GCC 7.2.1: during
optimization, the defined in C files interrupt functions are perceived as
unused and removed(replaced by its weak definitions) - I've checked that in the
.map file.
This issue does not occur when startup file is first on the source files list,
which is given as an argument to the linker. If I change order of source files,
all interrupt handlers from C files, that are placed on the source files list
before startup are removed and replaced by weak definitions from startup.
For me it seems that linker is removing interrupt handler functions before
noticing its usage in startup file. Or maybe weak function definitions from
startup override definitions from C files.
I've checked if this issue happens on the GCC 4.9.3 - it worked fine, so this
is rather new behaviour.
I've also confirmed this bug with other developer from Germany:
https://www.mikrocontroller.net/topic/443262
Take a look at the latest posts, which are written in English.
Is this a bug or should I place some extra pragmas/attributes to extort proper
linker behaviour?
Please let me know if you want me to prepare some basic examples of this issue.
