Why is compiler adding an extra 'sxtw' instruction (resulting further in a Kernel Panic)?ArchLinux kernel...
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Why is compiler adding an extra 'sxtw' instruction (resulting further in a Kernel Panic)?
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Issue/Symptom: At the end of a function return, compiler adds sxtw instruction as seen in the disassembly, resulting in a return address of only 32 bits instead of 64 bits, resulting in a kernel panic (Unable to handle kernel paging request at virtual address xxxx)
Build Environment:
Platform : ARMV7LE
gcc, linux-4.4.60
Arch : Arm64
gdb : aarch64-5.3-glibc-2.22/usr/bin/aarch64-linux-gdb
Details
Here's the simplified project structure.
It's been taken care of correctly in the corresponding makefile.
Also note that file1.c and file2.c are part of same module.
../src/file1.c /* It has func1() defined as well as called /
../src/file2.c
../inc/files.h / There's no func1() declared in the header */
Cause of the issue
A call to the func1() was added from the file2.c w/o func1 declaration in files.h or file2.c
(Basically the inclusion of func1 was accidentally missed in the files.h)
Code compiled with NO ERRORS but a warning as expected -- Implicit declaration of function func1.
At the run time though, right after returning from func1 inside file2, system crashed as it tried de-referencing the returned address from func1.
Further analysis showed that at the end of a function return, compiler added sxtw instruction as seen in the disassembly, resulting in a return address of only 32 bits instead of 64 bits, resulting in a kernel panic (Unable to handle kernel paging request at virtual address xxxx)
- Note that x19 is of 64 bit while w0 is of 32 bit.
- Note that x0 LS word matches with that of x19
- System crashed while de-referencing x19
sxtw x19, w0 /* This was added by compiler as extra instruction /
ldp x1, x0, [x19,#304] / System crashed here */
Registers :-
[ 91.388130] pc : [] lr : [] pstate: 80000145
[ 91.462090] sp : ffffff80094333b0
[ 91.552708] x29: ffffff80094333d0 x28: ffffffc06995408a
[ 91.652701] x27: ffffffc06c400a00 x26: 0000000000000000
[ 91.716243] x25: 0000000000000000 x24: ffffffc069958000
[ 91.779784] x23: ffffffc076e00000 x22: ffffffc06c400a00
[ 91.843326] x21: 0000000000000031 x20: ffffffc073060000
[ 91.906867] x19: 0000000066bfc780 x18: ffffff8009436888
[ 91.970409] x17: 0000000000000000 x16: ffffff8008193074
[ 92.033952] x15: 00000000000a8c06 x14: 2c30323030387830
[ 92.097492] x13: 3d7367616c66202c x12: 3038653030303030
[ 92.161034] x11: 3038666666666666 x10: 78303d646e65202c
[ 92.224576] x9 : 3063303030303030 x8 : 3030303030303030
[ 92.288117] x7 : 0000000000000880 x6 : 0000000000000000
[ 92.351659] x5 : ffffffc07fd10ad8 x4 : 0000000000000001
[ 92.415202] x3 : 0000000000000007 x2 : cb88537fdc8ba63c
[ 92.478743] x1 : 0000000000000000 x0 : ffffffc066bfc780
After adding the declaration of func1 in the files.h, the extra instruction and hence the crash was NOT seen.
Can someone please explain as to why the compiler added sxtw in this case?
linux 64-bit gcc arm
asked 3 mins ago
user1012064user1012064
1
New contributor
user1012064 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
Issue/Symptom: At the end of a function return, compiler adds sxtw instruction as seen in the disassembly, resulting in a return address of only 32 bits instead of 64 bits, resulting in a kernel panic (Unable to handle kernel paging request at virtual address xxxx)
Build Environment:
Platform : ARMV7LE
gcc, linux-4.4.60
Arch : Arm64
gdb : aarch64-5.3-glibc-2.22/usr/bin/aarch64-linux-gdb
Details
Here's the simplified project structure.
It's been taken care of correctly in the corresponding makefile.
Also note that file1.c and file2.c are part of same module.
../src/file1.c /* It has func1() defined as well as called /
../src/file2.c
../inc/files.h / There's no func1() declared in the header */
Cause of the issue
A call to the func1() was added from the file2.c w/o func1 declaration in files.h or file2.c
(Basically the inclusion of func1 was accidentally missed in the files.h)
Code compiled with NO ERRORS but a warning as expected -- Implicit declaration of function func1.
At the run time though, right after returning from func1 inside file2, system crashed as it tried de-referencing the returned address from func1.
Further analysis showed that at the end of a function return, compiler added sxtw instruction as seen in the disassembly, resulting in a return address of only 32 bits instead of 64 bits, resulting in a kernel panic (Unable to handle kernel paging request at virtual address xxxx)
- Note that x19 is of 64 bit while w0 is of 32 bit.
- Note that x0 LS word matches with that of x19
- System crashed while de-referencing x19
sxtw x19, w0 /* This was added by compiler as extra instruction /
ldp x1, x0, [x19,#304] / System crashed here */
Registers :-
[ 91.388130] pc : [] lr : [] pstate: 80000145
[ 91.462090] sp : ffffff80094333b0
[ 91.552708] x29: ffffff80094333d0 x28: ffffffc06995408a
[ 91.652701] x27: ffffffc06c400a00 x26: 0000000000000000
[ 91.716243] x25: 0000000000000000 x24: ffffffc069958000
[ 91.779784] x23: ffffffc076e00000 x22: ffffffc06c400a00
[ 91.843326] x21: 0000000000000031 x20: ffffffc073060000
[ 91.906867] x19: 0000000066bfc780 x18: ffffff8009436888
[ 91.970409] x17: 0000000000000000 x16: ffffff8008193074
[ 92.033952] x15: 00000000000a8c06 x14: 2c30323030387830
[ 92.097492] x13: 3d7367616c66202c x12: 3038653030303030
[ 92.161034] x11: 3038666666666666 x10: 78303d646e65202c
[ 92.224576] x9 : 3063303030303030 x8 : 3030303030303030
[ 92.288117] x7 : 0000000000000880 x6 : 0000000000000000
[ 92.351659] x5 : ffffffc07fd10ad8 x4 : 0000000000000001
[ 92.415202] x3 : 0000000000000007 x2 : cb88537fdc8ba63c
[ 92.478743] x1 : 0000000000000000 x0 : ffffffc066bfc780
After adding the declaration of func1 in the files.h, the extra instruction and hence the crash was NOT seen.
Can someone please explain as to why the compiler added sxtw in this case?
linux 64-bit gcc arm
asked 3 mins ago
user1012064user1012064
1
New contributor
user1012064 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
Issue/Symptom: At the end of a function return, compiler adds sxtw instruction as seen in the disassembly, resulting in a return address of only 32 bits instead of 64 bits, resulting in a kernel panic (Unable to handle kernel paging request at virtual address xxxx)
Build Environment:
Platform : ARMV7LE
gcc, linux-4.4.60
Arch : Arm64
gdb : aarch64-5.3-glibc-2.22/usr/bin/aarch64-linux-gdb
Details
Here's the simplified project structure.
It's been taken care of correctly in the corresponding makefile.
Also note that file1.c and file2.c are part of same module.
../src/file1.c /* It has func1() defined as well as called /
../src/file2.c
../inc/files.h / There's no func1() declared in the header */
Cause of the issue
A call to the func1() was added from the file2.c w/o func1 declaration in files.h or file2.c
(Basically the inclusion of func1 was accidentally missed in the files.h)
Code compiled with NO ERRORS but a warning as expected -- Implicit declaration of function func1.
At the run time though, right after returning from func1 inside file2, system crashed as it tried de-referencing the returned address from func1.
Further analysis showed that at the end of a function return, compiler added sxtw instruction as seen in the disassembly, resulting in a return address of only 32 bits instead of 64 bits, resulting in a kernel panic (Unable to handle kernel paging request at virtual address xxxx)
- Note that x19 is of 64 bit while w0 is of 32 bit.
- Note that x0 LS word matches with that of x19
- System crashed while de-referencing x19
sxtw x19, w0 /* This was added by compiler as extra instruction /
ldp x1, x0, [x19,#304] / System crashed here */
Registers :-
[ 91.388130] pc : [] lr : [] pstate: 80000145
[ 91.462090] sp : ffffff80094333b0
[ 91.552708] x29: ffffff80094333d0 x28: ffffffc06995408a
[ 91.652701] x27: ffffffc06c400a00 x26: 0000000000000000
[ 91.716243] x25: 0000000000000000 x24: ffffffc069958000
[ 91.779784] x23: ffffffc076e00000 x22: ffffffc06c400a00
[ 91.843326] x21: 0000000000000031 x20: ffffffc073060000
[ 91.906867] x19: 0000000066bfc780 x18: ffffff8009436888
[ 91.970409] x17: 0000000000000000 x16: ffffff8008193074
[ 92.033952] x15: 00000000000a8c06 x14: 2c30323030387830
[ 92.097492] x13: 3d7367616c66202c x12: 3038653030303030
[ 92.161034] x11: 3038666666666666 x10: 78303d646e65202c
[ 92.224576] x9 : 3063303030303030 x8 : 3030303030303030
[ 92.288117] x7 : 0000000000000880 x6 : 0000000000000000
[ 92.351659] x5 : ffffffc07fd10ad8 x4 : 0000000000000001
[ 92.415202] x3 : 0000000000000007 x2 : cb88537fdc8ba63c
[ 92.478743] x1 : 0000000000000000 x0 : ffffffc066bfc780
After adding the declaration of func1 in the files.h, the extra instruction and hence the crash was NOT seen.
Can someone please explain as to why the compiler added sxtw in this case?
linux 64-bit gcc arm
asked 3 mins ago
user1012064user1012064
1
New contributor
user1012064 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Issue/Symptom: At the end of a function return, compiler adds sxtw instruction as seen in the disassembly, resulting in a return address of only 32 bits instead of 64 bits, resulting in a kernel panic (Unable to handle kernel paging request at virtual address xxxx)
Build Environment:
Platform : ARMV7LE
gcc, linux-4.4.60
Arch : Arm64
gdb : aarch64-5.3-glibc-2.22/usr/bin/aarch64-linux-gdb
Details
Here's the simplified project structure.
It's been taken care of correctly in the corresponding makefile.
Also note that file1.c and file2.c are part of same module.
../src/file1.c /* It has func1() defined as well as called /
../src/file2.c
../inc/files.h / There's no func1() declared in the header */
Cause of the issue
A call to the func1() was added from the file2.c w/o func1 declaration in files.h or file2.c
(Basically the inclusion of func1 was accidentally missed in the files.h)
Code compiled with NO ERRORS but a warning as expected -- Implicit declaration of function func1.
At the run time though, right after returning from func1 inside file2, system crashed as it tried de-referencing the returned address from func1.
Further analysis showed that at the end of a function return, compiler added sxtw instruction as seen in the disassembly, resulting in a return address of only 32 bits instead of 64 bits, resulting in a kernel panic (Unable to handle kernel paging request at virtual address xxxx)
- Note that x19 is of 64 bit while w0 is of 32 bit.
- Note that x0 LS word matches with that of x19
- System crashed while de-referencing x19
sxtw x19, w0 /* This was added by compiler as extra instruction /
ldp x1, x0, [x19,#304] / System crashed here */
Registers :-
[ 91.388130] pc : [] lr : [] pstate: 80000145
[ 91.462090] sp : ffffff80094333b0
[ 91.552708] x29: ffffff80094333d0 x28: ffffffc06995408a
[ 91.652701] x27: ffffffc06c400a00 x26: 0000000000000000
[ 91.716243] x25: 0000000000000000 x24: ffffffc069958000
[ 91.779784] x23: ffffffc076e00000 x22: ffffffc06c400a00
[ 91.843326] x21: 0000000000000031 x20: ffffffc073060000
[ 91.906867] x19: 0000000066bfc780 x18: ffffff8009436888
[ 91.970409] x17: 0000000000000000 x16: ffffff8008193074
[ 92.033952] x15: 00000000000a8c06 x14: 2c30323030387830
[ 92.097492] x13: 3d7367616c66202c x12: 3038653030303030
[ 92.161034] x11: 3038666666666666 x10: 78303d646e65202c
[ 92.224576] x9 : 3063303030303030 x8 : 3030303030303030
[ 92.288117] x7 : 0000000000000880 x6 : 0000000000000000
[ 92.351659] x5 : ffffffc07fd10ad8 x4 : 0000000000000001
[ 92.415202] x3 : 0000000000000007 x2 : cb88537fdc8ba63c
[ 92.478743] x1 : 0000000000000000 x0 : ffffffc066bfc780
After adding the declaration of func1 in the files.h, the extra instruction and hence the crash was NOT seen.
Can someone please explain as to why the compiler added sxtw in this case?
linux 64-bit gcc arm
linux 64-bit gcc arm
asked 3 mins ago
user1012064user1012064
1
New contributor
user1012064 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 3 mins ago
user1012064user1012064
1
New contributor
user1012064 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 3 mins ago
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user1012064 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 3 mins ago
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asked 3 mins ago
user1012064user1012064
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user1012064 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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user1012064 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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Check out our Code of Conduct.
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