This revision was automatically updated to reflect the committed changes.
Closed by commit rG7e8af2fc0c06: [ARM] Support -mexecute-only with
-mlong-calls. (authored by ZhiyaoMa98, committed by efriedma).
Changed prior to commit:
https://reviews.llvm.org/D136203?vs=469049&id=470236#toc
Reposito
ZhiyaoMa98 added a comment.
Just in case you assume that I have push permission, unfortunately I do not.
Could you help me merge the patch in? Thanks.
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ZhiyaoMa98 updated this revision to Diff 469049.
ZhiyaoMa98 marked an inline comment as done.
ZhiyaoMa98 added a comment.
Remove the unused `GA` variable.
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Files:
clang/lib/Driver/ToolChains/Arc
ZhiyaoMa98 updated this revision to Diff 468973.
ZhiyaoMa98 marked an inline comment as done.
ZhiyaoMa98 added a comment.
Updated the comment to reflect that now we allow using `-mlong-calls` with
`-mexecute-only`.
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https://revie
efriedma accepted this revision.
efriedma added a comment.
This revision is now accepted and ready to land.
LGTM with one small change.
Comment at: clang/lib/Driver/ToolChains/Arch/ARM.cpp:779
// Supported only on ARMv6T2 and ARMv7 and above.
// Cannot be combined wit
ZhiyaoMa98 added a comment.
> Then just assert we aren't execute-only in the non-movw path.
When we are not execute-only, existing code handles it by using constant pools
and we are all good.
In the case where we are execute-only and long-calls at the same time, we
assert that we have `movt` l
ZhiyaoMa98 updated this revision to Diff 468957.
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Files:
clang/lib/Driver/ToolChains/Arch/ARM.cpp
clang/test/Driver/arm-execute-only.c
llvm/lib/Target/ARM/ARMISelLowering.cpp
llvm/test/CodeG
efriedma added a comment.
> I am thinking about adding a new option, say -mgot-calls to allow code
> generation with the extra indirection. Is it sensible and shall I create
> another diff to discuss that?
That probably makes sense, yes.
Comment at: llvm/lib/Target/ARM/ARMIS
ZhiyaoMa98 marked an inline comment as done.
ZhiyaoMa98 added a comment.
I have updated the diff to avoid the extra indirection. I am thinking about
adding a new option, say `-mgot-calls` to allow code generation with the extra
indirection. Is it sensible and shall I create another diff to discu
ZhiyaoMa98 updated this revision to Diff 468928.
ZhiyaoMa98 edited the summary of this revision.
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Files:
clang/lib/Driver/ToolChains/Arch/ARM.cpp
clang/test/Driver/arm-execute-only.c
llvm/lib/
efriedma added a comment.
One, -mlong-calls isn't currently compatible with PIE. Two, on ARM, there are
no special plt relocations; the linker just takes care of it. (You can see the
differences if you try to take the address of a function without calling it.)
Repository:
rG LLVM Github Mo
ZhiyaoMa98 added a comment.
Unfortunately, `-fPIE` seems not to be generating the PLT on LLVM for embedded
ARM.
C source file (test.c):
extern void bar(void);
void foo(void) {
bar();
}
LLVM with `clang -O2 -fPIE -fsemantic-interposition -mlong-calls
--target=armv7em-none-eabi -c t
efriedma added a comment.
The construct you want is pretty similar to a GOT. if you compile with -fPIE
-fsemantic-interposition, you get basically the code you want, except that the
compiler uses a plt by default instead of a got. If we supported -fno-plt for
ARM, it would be almost exactly wh
ZhiyaoMa98 added a comment.
> Can you describe a little more what you're trying to do here?
Sure. My eventual goal is to enable fine-granular live-update on ARM based
microcontrollers, which requires the system to do some relocation at runtime.
Below I will describe the challenge with a simple
efriedma added a comment.
> that I can redirect the function call at runtime, for dynamic linking purpose.
Can you describe a little more what you're trying to do here?
If you want to replace the implementation of an existing function at runtime,
you'd be better off implementing the indirection
ZhiyaoMa98 added a comment.
@efriedma Thank you for your suggestion. I will remove the extra indirection.
I was wondering if you could also provide some insights about the RWPI case. I
believe the same optimization also applies to RWPI. However, I actually want to
store the function address as
efriedma added inline comments.
Comment at: llvm/test/CodeGen/Thumb2/thumb2-execute-only-long-calls.ll:19
+; STATIC-NEXT: movt[[REG0]], :upper16:.LCP1_0
+; STATIC-NEXT: ldr [[REG1:r[0-9]+]], [[[REG0]]]
+; STATIC-NEXT: blx [[REG1]]
Is there some rea
ZhiyaoMa98 created this revision.
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