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lldb: Show consistent stack pointer value with GDB
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I was tested this patch on following OpenBSD 7.7-current:
$ sysctl -n kern.version
OpenBSD 7.7-current (GENERIC.MP) #0: Sat May 24 17:12:34 JST 2025
asou@obsd-lldb.soum.co.jp:/usr/src/sys/arch/amd64/compile/GENERIC.MP
$
--
ASOU@j2k25
On Fri, Nov 22, 2024 at 12:46 PM ASOU Masato <takeasou.masato@gmail.com> wrote:
>
> I made a mistake when applying Naito's patch.
> Broken lldb:
>
> $ doas lldb bsd.0 -c bsd.0.core
> doas (asou@asou-lldb-kernel.soum.co.jp) password:
> (lldb) target create "bsd.0" --core "bsd.0.core"
> Core file '/var/crash/bsd.0.core' (x86_64) was loaded.
> (lldb) register read
> General Purpose Registers:
> rbp = 0xffff80001cb01ca0
> rsp = 0xffff80001cb01a50
> rip = 0xffff80001cb01cd0
> ^^^^^^^^^^^^^^^^^^ This is stack area.
> 21 registers were unavailable.
>
> (lldb) bt
> * thread #1, name = 'Crashed Thread'
> * frame #0: 0xffff80001cb01cd0
> frame #1: 0xffffffff8188f51c bsd.0`boot + 268
> frame #2: 0xffffffff81750548 bsd.0`reboot + 104
> frame #3: 0xffffffff817504da bsd.0`sys_reboot + 154
> frame #4: 0xffffffff81597807 bsd.0`syscall + 1511
> frame #5: 0xffffffff82312134 bsd.0`Xsyscall_meltdown + 308
> frame #6: 0xffffffff82312055 bsd.0`Xsyscall_meltdown + 85
> frame #7: 0xffff80001cb01e00
> frame #8: 0x0000083fba322fab
> (lldb)
>
>
> And I corrected mistake.
> Corrected lldb:
>
> $ doas lldb bsd.0 -c bsd.0.core
> doas (asou@asou-lldb-kernel.soum.co.jp) password:
> (lldb) target create "bsd.0" --core "bsd.0.core"
> Core file '/var/crash/bsd.0.core' (x86_64) was loaded.
> (lldb) register read
> General Purpose Registers:
> rbp = 0xffff80001cb01ca0
> rsp = 0xffff80001cb01a50
> rip = 0xffffffff8188fda3 bsd.0`dumpsys + 1795
> ^^^^^^^^^^^^^^^^^^ This is instruction area.
> 21 registers were unavailable.
>
> (lldb) bt
> * thread #1, name = 'Crashed Thread'
> * frame #0: 0xffffffff8188fda3 bsd.0`dumpsys + 1795
> frame #1: 0xffffffff8188f51c bsd.0`boot + 268
> frame #2: 0xffffffff81750548 bsd.0`reboot + 104
> frame #3: 0xffffffff817504da bsd.0`sys_reboot + 154
> frame #4: 0xffffffff81597807 bsd.0`syscall + 1511
> frame #5: 0xffffffff82312134 bsd.0`Xsyscall_meltdown + 308
> frame #6: 0xffffffff82312055 bsd.0`Xsyscall_meltdown + 85
> frame #7: 0xffff80001cb01e00
> frame #8: 0x0000083fba322fab
> (lldb)
>
> ok, comments?
> --
> ASOU Masato
>
> Index: gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_i386.cpp
> ===================================================================
> RCS file: /cvs/src/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_i386.cpp,v
> diff -u -p -r1.2 RegisterContextOpenBSDKernel_i386.cpp
> --- gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_i386.cpp
> 31 Oct 2024 07:37:35 -0000 1.2
> +++ gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_i386.cpp
> 22 Nov 2024 03:43:08 -0000
> @@ -62,12 +62,12 @@ bool RegisterContextOpenBSDKernel_i386::
> if ((pcb.pcb_flags & PCB_SAVECTX) != 0) {
> uint32_t reg = reg_info->kinds[lldb::eRegisterKindLLDB];
> switch (reg) {
> - return true;
> case lldb_esp_i386:
> value = (u_int32_t)pcb.pcb_ebp;
> return true;
> case lldb_ebp_i386:
> value = m_thread.GetProcess()->ReadPointerFromMemory(pcb.pcb_ebp, error);
> + return true;
> case lldb_eip_i386:
> value = m_thread.GetProcess()->ReadPointerFromMemory(pcb.pcb_ebp + 4,
> error);
> @@ -88,21 +88,21 @@ bool RegisterContextOpenBSDKernel_i386::
>
> uint32_t reg = reg_info->kinds[lldb::eRegisterKindLLDB];
> switch (reg) {
> -#define PCBREG(x, offset) \
> - case lldb_##x##_i386: \
> - value = (u_int32_t)(pcb.pcb_##x + (offset)); \
> +#define PCBREG(x, offset) \
> + case lldb_##x##_i386: \
> + value = (u_int32_t)(pcb.pcb_##x + (offset)); \
> return true;
> #define SFREG(x) \
> case lldb_##x##_i386: \
> - value = sf.sf_##x; \
> + value = (u_int32_t)sf.sf_##x; \
> return true;
>
> SFREG(edi);
> SFREG(esi);
> SFREG(ebx);
> SFREG(eip);
> - PCBREG(ebp);
> - PCBREG(esp);
> + PCBREG(ebp, 0);
> + PCBREG(esp, sizeof(sf));
> }
> #endif
> return false;
> Index: gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_x86_64.cpp
> ===================================================================
> RCS file: /cvs/src/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_x86_64.cpp,v
> diff -u -p -r1.2 RegisterContextOpenBSDKernel_x86_64.cpp
> --- gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_x86_64.cpp
> 31 Oct 2024 07:37:35 -0000 1.2
> +++ gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_x86_64.cpp
> 22 Nov 2024 03:43:08 -0000
> @@ -96,7 +96,7 @@ bool RegisterContextOpenBSDKernel_x86_64
> PCBREG(rbp, 0);
> PCBREG(rsp, 8);
> case lldb_rip_x86_64:
> - value = m_thread.GetProcess()->ReadPointerFromMemory(pcb.pcb_rbp, error);
> + value = m_thread.GetProcess()->ReadPointerFromMemory(pcb.pcb_rsp, error);
> return true;
> }
> }
>
> On Thu, Oct 31, 2024 at 8:13 AM ASOU Masato <takeasou.masato@gmail.com> wrote:
> >
> > There are no objections, so I will commit later.
> > --
> > ASOU Masato
> >
> > On Fri, Oct 18, 2024 at 10:35 AM ASOU Masato <takeasou.masato@gmail.com> wrote:
> > >
> > > Hi robert and list.
> > >
> > > I was tested this patch on amd64 box and work fine for me.
> > > ok asou@
> > >
> > > Can I commit this patch ok?
> > >
> > > Before apply patch:
> > > $ cd /var/crash
> > > $ doas gdb bsd.0
> > > GNU gdb 6.3
> > > Copyright 2004 Free Software Foundation, Inc.
> > > GDB is free software, covered by the GNU General Public License, and you are
> > > welcome to change it and/or distribute copies of it under certain
> > > conditions.
> > > Type "show copying" to see the conditions.
> > > There is absolutely no warranty for GDB. Type "show warranty" for details.
> > > This GDB was configured as "amd64-unknown-openbsd7.6"...(no
> > > debugging symbols found)
> > >
> > > (gdb) target kvm bsd.0.core
> > > #0 0xffffffff8188fda3 in dumpsys ()
> > > (gdb) info register
> > >
> > > </snip>
> > >
> > > rbp 0xffff80001cb01ca0 0xffff80001cb01ca0
> > > rsp 0xffff80001cb01a50 0xffff80001cb01a50
> > >
> > > </snip>
> > >
> > > (gdb) quit
> > > $ doas lldb bsd.0 -c bsd.0.core
> > > (lldb) target create "bsd.0" --core "bsd.0.core"
> > > Core file '/var/crash/bsd.0.core' (x86_64) was loaded.
> > > (lldb) bt
> > > * thread #1, name = 'Crashed Thread'
> > > * frame #0: 0xffffffff8188f51c bsd.0`boot + 268
> > > frame #1: 0xffffffff8188f51c bsd.0`boot + 268
> > > frame #2: 0xffffffff81750548 bsd.0`reboot + 104
> > > frame #3: 0xffffffff817504da bsd.0`sys_reboot + 154
> > > frame #4: 0xffffffff81597807 bsd.0`syscall + 1511
> > > frame #5: 0xffffffff82312134 bsd.0`Xsyscall_meltdown + 308
> > > frame #6: 0xffffffff82312055 bsd.0`Xsyscall_meltdown + 85
> > > frame #7: 0xffff80001cb01e00
> > > frame #8: 0x0000083fba322fab
> > > (lldb) register read
> > > General Purpose Registers:
> > > rbp = 0xffff80001cb01ca0
> > > rsp = 0xffff80001cb01a48
> > > rip = 0xffffffff8188f51c bsd.0`boot + 268
> > > 21 registers were unavailable.
> > >
> > > (lldb) quit
> > >
> > > After applay patch:
> > > $ doas lldb bsd.0 -c bsd.0.core
> > > doas (asou@asou-lldb-kernel.soum.co.jp) password:
> > > (lldb) target create "bsd.0" --core "bsd.0.core"
> > > Core file '/var/crash/bsd.0.core' (x86_64) was loaded.
> > > (lldb) bt
> > > * thread #1, name = 'Crashed Thread'
> > > * frame #0: 0xffff80001cb01cd0
> > > frame #1: 0xffffffff8188f51c bsd.0`boot + 268
> > > frame #2: 0xffffffff81750548 bsd.0`reboot + 104
> > > frame #3: 0xffffffff817504da bsd.0`sys_reboot + 154
> > > frame #4: 0xffffffff81597807 bsd.0`syscall + 1511
> > > frame #5: 0xffffffff82312134 bsd.0`Xsyscall_meltdown + 308
> > > frame #6: 0xffffffff82312055 bsd.0`Xsyscall_meltdown + 85
> > > frame #7: 0xffff80001cb01e00
> > > frame #8: 0x0000083fba322fab
> > > (lldb) register read
> > > General Purpose Registers:
> > > rbp = 0xffff80001cb01ca0
> > > rsp = 0xffff80001cb01a50
> > > rip = 0xffff80001cb01cd0
> > > 21 registers were unavailable.
> > >
> > > (lldb)
> > > --
> > > ASOU Masato
> > >
> > > On Fri, Aug 30, 2024 at 6:22 PM Yuichiro NAITO <naito.yuichiro@gmail.com> wrote:
> > > >
> > > > While I see the top of the backtrace frame in the kernel core file,
> > > > the stack register value is differs from what GDB shows.
> > > >
> > > > For example, the kernel core file that is written by ddb, the stack pointer
> > > > of the crashed thread is saved by the 'savectx' function. GDB rollbacks
> > > > the pointer to the position when the beginning of the 'savectx' function is
> > > > called. The lldb in my code won't.
> > > >
> > > > The lldb shows as follows.
> > > >
> > > > ```
> > > > (lldb) register read
> > > > General Purpose Registers:
> > > > rbp = 0xffff80001c9e2460
> > > > rsp = 0xffff80001c9e2208
> > > > rip = 0xffffffff81adbc0c bsd.0`db_fncall + 1052
> > > > 21 registers were unavailable.
> > > > ```
> > > >
> > > > Gdb shows as follows.
> > > >
> > > > ```
> > > > (gdb) info registers
> > > > rax 0x0 0
> > > > rbx 0x0 0
> > > > rcx 0x0 0
> > > > rdx 0x0 0
> > > > rsi 0x0 0
> > > > rdi 0x0 0
> > > > rbp 0xffff80001c9e2460 0xffff80001c9e2460
> > > > rsp 0xffff80001c9e2210 0xffff80001c9e2210
> > > > r8 0x0 0
> > > > r9 0x0 0
> > > > r10 0x0 0
> > > > r11 0x0 0
> > > > r12 0x0 0
> > > > r13 0x0 0
> > > > r14 0x0 0
> > > > r15 0x0 0
> > > > rip 0xffffffff819f8723 0xffffffff819f8723 <dumpsys+1795>
> > > > eflags 0x0 0
> > > > cs 0x0 0
> > > > ss 0x0 0
> > > > ds 0x0 0
> > > > es 0x0 0
> > > > fs 0x0 0
> > > > gs 0x0 0
> > > > ```
> > > >
> > > > In this case, the lldb `rsp` value is 8 bytes smaller than what of gdb.
> > > > These 8 bytes are the return address from the 'savectx' function.
> > > > And `rip` is also different. It is my fault way to read it from `struct pcb`.
> > > > The 'savectx' function is called from the 'dumpsys' function so the GDB shows
> > > > the right pointer.
> > > >
> > > > In the other case, `struct pcb` is written by the 'cpu_switchto' function and
> > > > the same thing happens. I fixed these cases to be consistent with GDB
> > > > on amd64, i386, and arm64 architectures.
> > > > OK?
> > > >
> > > > diff --git a/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_arm64.cpp b/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_arm64.cpp
> > > > index 1ebfc6a799f..34fc8067203 100644
> > > > --- a/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_arm64.cpp
> > > > +++ b/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_arm64.cpp
> > > > @@ -91,7 +91,7 @@ bool RegisterContextOpenBSDKernel_arm64::ReadRegister(
> > > > value = (u_int64_t)sf.sf_x29;
> > > > return true;
> > > > case gpr_sp_arm64:
> > > > - value = (u_int64_t)pcb.pcb_sp;
> > > > + value = (u_int64_t)(pcb.pcb_sp + sizeof(sf));
> > > > return true;
> > > > case gpr_pc_arm64:
> > > > value = (u_int64_t)sf.sf_lr;
> > > > diff --git a/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_i386.cpp b/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_i386.cpp
> > > > index 9a909a4e07d..fcbe6d9000a 100644
> > > > --- a/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_i386.cpp
> > > > +++ b/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_i386.cpp
> > > > @@ -62,12 +62,13 @@ bool RegisterContextOpenBSDKernel_i386::ReadRegister(
> > > > if ((pcb.pcb_flags & PCB_SAVECTX) != 0) {
> > > > uint32_t reg = reg_info->kinds[lldb::eRegisterKindLLDB];
> > > > switch (reg) {
> > > > -#define PCBREG(x) \
> > > > - case lldb_##x##_i386: \
> > > > - value = pcb.pcb_##x; \
> > > > + case lldb_esp_i386:
> > > > + value = (u_int32_t)pcb.pcb_ebp;
> > > > + return true;
> > > > + case lldb_ebp_i386:
> > > > + value = m_thread.GetProcess()->ReadPointerFromMemory(pcb.pcb_ebp,
> > > > + error);
> > > > return true;
> > > > - PCBREG(ebp);
> > > > - PCBREG(esp);
> > > > case lldb_eip_i386:
> > > > value = m_thread.GetProcess()->ReadPointerFromMemory(pcb.pcb_ebp + 4,
> > > > error);
> > > > @@ -88,17 +89,21 @@ bool RegisterContextOpenBSDKernel_i386::ReadRegister(
> > > >
> > > > uint32_t reg = reg_info->kinds[lldb::eRegisterKindLLDB];
> > > > switch (reg) {
> > > > +#define PCBREG(x, offset) \
> > > > + case lldb_##x##_i386: \
> > > > + value = (u_int32_t)(pcb.pcb_##x + (offset)); \
> > > > + return true;
> > > > #define SFREG(x) \
> > > > case lldb_##x##_i386: \
> > > > - value = sf.sf_##x; \
> > > > + value = (u_int32_t)sf.sf_##x; \
> > > > return true;
> > > >
> > > > SFREG(edi);
> > > > SFREG(esi);
> > > > SFREG(ebx);
> > > > SFREG(eip);
> > > > - PCBREG(ebp);
> > > > - PCBREG(esp);
> > > > + PCBREG(ebp, 0);
> > > > + PCBREG(esp, sizeof(sf));
> > > > }
> > > > #endif
> > > > return false;
> > > > diff --git a/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_x86_64.cpp b/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_x86_64.cpp
> > > > index 501fa858a92..a5eff4f42cf 100644
> > > > --- a/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_x86_64.cpp
> > > > +++ b/gnu/llvm/lldb/source/Plugins/Process/OpenBSDKernel/RegisterContextOpenBSDKernel_x86_64.cpp
> > > > @@ -77,9 +77,9 @@ bool RegisterContextOpenBSDKernel_x86_64::ReadRegister(
> > > > case lldb_##x##_x86_64: \
> > > > value = (u_int64_t)sf.sf_##x; \
> > > > return true;
> > > > -#define PCBREG(x) \
> > > > +#define PCBREG(x, offset) \
> > > > case lldb_##x##_x86_64: \
> > > > - value = pcb.pcb_##x; \
> > > > + value = pcb.pcb_##x + (offset); \
> > > > return true;
> > > > switch (reg) {
> > > > SFREG(r15);
> > > > @@ -89,14 +89,14 @@ bool RegisterContextOpenBSDKernel_x86_64::ReadRegister(
> > > > SFREG(rbp);
> > > > SFREG(rbx);
> > > > SFREG(rip);
> > > > - PCBREG(rsp);
> > > > + PCBREG(rsp, sizeof(sf));
> > > > }
> > > > } else {
> > > > switch (reg) {
> > > > - PCBREG(rbp);
> > > > - PCBREG(rsp);
> > > > + PCBREG(rbp, 0);
> > > > + PCBREG(rsp, 8);
> > > > case lldb_rip_x86_64:
> > > > - value = m_thread.GetProcess()->ReadPointerFromMemory(pcb.pcb_rbp + 8,
> > > > + value = m_thread.GetProcess()->ReadPointerFromMemory(pcb.pcb_rsp,
> > > > error);
> > > > return true;
> > > > }
> > > >
> > > > --
> > > > Yuichiro NAITO (naito.yuichiro@gmail.com)
> > > >
lldb: Show consistent stack pointer value with GDB