Commit e3d8ee35e4 ("reland "[DebugInfo] Support to emit debugInfo
for extern variables"") added support to emit debugInfo for
extern variables if requested by the target. Currently, only
BPF target enables this feature by default.
As BPF ecosystem grows, callback function started to get
support, e.g., recently bpf_for_each_map_elem() is introduced
(https://lwn.net/Articles/846504/) with a callback function as an
argument. In the future we may have something like below as
a demonstration of use case :
extern int do_work(int);
long bpf_helper(void *callback_fn, void *callback_ctx, ...);
long prog_main() {
struct { ... } ctx = { ... };
return bpf_helper(&do_work, &ctx, ...);
}
Basically bpf helper may have a callback function and the
callback function is defined in another file or in the kernel.
In this case, we would like to know the debuginfo types for
do_work(), so the verifier can proper verify the safety of
bpf_helper() call.
For the following example,
extern int do_work(int);
long bpf_helper(void *callback_fn);
long prog() {
return bpf_helper(&do_work);
}
Currently, there is no debuginfo generated for extern function do_work().
In the IR, we have,
...
define dso_local i64 @prog() local_unnamed_addr #0 !dbg !7 {
entry:
%call = tail call i64 @bpf_helper(i8* bitcast (i32 (i32)* @do_work to i8*)) #2, !dbg !11
ret i64 %call, !dbg !12
}
...
declare dso_local i32 @do_work(i32) #1
...
This patch added support for the above callback function use case, and
the generated IR looks like below:
...
declare !dbg !17 dso_local i32 @do_work(i32) #1
...
!17 = !DISubprogram(name: "do_work", scope: !1, file: !1, line: 1, type: !18, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
!18 = !DISubroutineType(types: !19)
!19 = !{!20, !20}
!20 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
The TargetInfo.allowDebugInfoForExternalVar is renamed to
TargetInfo.allowDebugInfoForExternalRef as now it guards
both extern variable and extern function debuginfo generation.
Differential Revision: https://reviews.llvm.org/D100567
Currently, bpf does not specify 128bit alignment in its
layout spec. So for a structure like
struct ipv6_key_t {
unsigned pid;
unsigned __int128 saddr;
unsigned short lport;
};
clang will generate IR type
%struct.ipv6_key_t = type { i32, [12 x i8], i128, i16, [14 x i8] }
Additional padding is to ensure later IR->MIR can generate correct
stack layout with target layout spec.
But it is common practice for a tracing program to be
first compiled with target flag (e.g., x86_64 or aarch64) through
clang to generate IR and then go through llc to generate bpf
byte code. Tracing program often refers to kernel internal
data structures which needs to be compiled with non-bpf target.
But such a compilation model may cause a problem on aarch64.
The bcc issue https://github.com/iovisor/bcc/issues/2827
reported such a problem.
For the above structure, since aarch64 has "i128:128" in its
layout string, the generated IR will have
%struct.ipv6_key_t = type { i32, i128, i16 }
Since bpf does not have "i128:128" in its spec string,
the selectionDAG assumes alignment 8 for i128 and
computes the stack storage size for the above is 32 bytes,
which leads incorrect code later.
The x86_64 does not have this issue as it does not have
"i128:128" in its layout spec as it does permits i128 to
be alignmented at 8 bytes at stack. Its IR type looks like
%struct.ipv6_key_t = type { i32, [12 x i8], i128, i16, [14 x i8] }
The fix here is add i128 support in layout spec, the same as
aarch64. The only downside is we may have less optimal stack
allocation in certain cases since we require 16byte alignment
for i128 instead of 8. But this is probably fine as i128 is
not used widely and in most cases users should already
have proper alignment.
Differential Revision: https://reviews.llvm.org/D76587
Commit d77ae1552f
("[DebugInfo] Support to emit debugInfo for extern variables")
added deebugInfo for extern variables for BPF target.
The commit is reverted by 891e25b02d
as the committed tests using %clang instead of %clang_cc1 causing
test failed in certain scenarios as reported by Reid Kleckner.
This patch fixed the tests by using %clang_cc1.
Differential Revision: https://reviews.llvm.org/D71818
Extern variable usage in BPF is different from traditional
pure user space application. Recent discussion in linux bpf
mailing list has two use cases where debug info types are
required to use extern variables:
- extern types are required to have a suitable interface
in libbpf (bpf loader) to provide kernel config parameters
to bpf programs.
https://lore.kernel.org/bpf/CAEf4BzYCNo5GeVGMhp3fhysQ=_axAf=23PtwaZs-yAyafmXC9g@mail.gmail.com/T/#t
- extern types are required so kernel bpf verifier can
verify program which uses external functions more precisely.
This will make later link with actual external function no
need to reverify.
https://lore.kernel.org/bpf/87eez4odqp.fsf@toke.dk/T/#m8d5c3e87ffe7f2764e02d722cb0d8cbc136880ed
This patch added clang support to emit debuginfo for extern variables
with a TargetInfo hook to enable it. The debuginfo for the
extern variable is emitted only if that extern variable is
referenced in the current compilation unit.
Currently, only BPF target enables to generate debug info for
extern variables. The emission of such debuginfo is disabled for C++
at this moment since BPF only supports a subset of C language.
Emission with C++ can be enabled later if an appropriate use case
is identified.
-fstandalone-debug permits us to see more debuginfo with the cost
of bloated binary size. This patch did not add emission of extern
variable debug info with -fstandalone-debug. This can be
re-evaluated if there is a real need.
Differential Revision: https://reviews.llvm.org/D70696
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
Sometimes when people compile bpf programs with
"clang ... -target bpf ...", the kernel header
files may contain host arch inline assembly codes
as in the patch https://patchwork.kernel.org/patch/10119683/
by Arnaldo Carvaldo de Melo.
The current workaround in the above patch
is to guard the inline assembly with "#ifndef __BPF__"
marco. So when __BPF__ is defined, these macros will
have no use.
Such a method is not extensible. As a matter of fact,
most of these inline assembly codes will be thrown away
at the end of clang compilation.
So for bpf target, this patch accepts all asm register
names in clang AST stage. The name will be checked
again during llc code generation if the inline assembly
code is indeed for bpf programs.
With this patch, the above "#ifndef __BPF__" is not needed
any more in https://patchwork.kernel.org/patch/10119683/.
Signed-off-by: Yonghong Song <yhs@fb.com>
llvm-svn: 329823
LLVM has supported a new target feature "alu32" which could be enabled or
disabled by "-mattr=[+|-]alu32" when using llc.
This patch link Clang with it, so it could be also done by passing related
options to Clang, for example:
-Xclang -target-feature -Xclang +alu32
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Yonghong Song <yhs@fb.com>
llvm-svn: 325996
Targets.cpp is getting unwieldy, and even minor changes cause the entire thing
to cause recompilation for everyone. This patch bites the bullet and breaks
it up into a number of files.
I tended to keep function definitions in the class declaration unless it
caused additional includes to be necessary. In those cases, I pulled it
over into the .cpp file. Content is copy/paste for the most part,
besides includes/format/etc.
Differential Revision: https://reviews.llvm.org/D35701
llvm-svn: 308791
Alessandro Decina