| Message ID | c2bbbe2ac9f41c19f746418df324212b2e4684a5.1720799487.git.oleksii.kurochko@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | RISCV basic exception handling implementation | expand |
On 12.07.2024 18:18, Oleksii Kurochko wrote: > To have working BUG(), WARN(), ASSERT, run_in_exception_handler() > it is needed to enable GENERIC_BUG_FRAME. > > Also, <xen/lib.h> is needed to be included for the reason that panic() and > printk() are used in common/bug.c and RISC-V fails if it is not included > with the following errors: > common/bug.c:69:9: error: implicit declaration of function 'printk' > [-Werror=implicit-function-declaration] > 69 | printk("Xen WARN at %s%s:%d\n", prefix, filename, > lineno); > | ^~~~~~ > common/bug.c:77:9: error: implicit declaration of function 'panic' > [-Werror=implicit-function-declaration] > 77 | panic("Xen BUG at %s%s:%d\n", prefix, filename, > lineno); I don't think the diagnostics themselves are needed here. > Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com> > --- > Changes in V10: > - put 'select GENERIC_BUG_FRAME' in "Config RISCV". > - rework do_trap() to not fetch an instruction in case when the cause of trap > is BUG_insn. It's BUG_insn here, but then ... > @@ -103,7 +104,29 @@ static void do_unexpected_trap(const struct cpu_user_regs *regs) > > void do_trap(struct cpu_user_regs *cpu_regs) > { > - do_unexpected_trap(cpu_regs); > + register_t pc = cpu_regs->sepc; > + unsigned long cause = csr_read(CSR_SCAUSE); > + > + switch ( cause ) > + { > + case CAUSE_BREAKPOINT: ... BREAKPOINT here? Generally I'd deem something named "breakpoint" as debugging related (and hence continuable). I'd have expected CAUSE_ILLEGAL_INSTRUCTION here, but likely I'm missing something. > + if ( do_bug_frame(cpu_regs, pc) >= 0 ) > + { > + if ( !pc || In how far does this really need special casing? Isn't that case covered by > + !(is_kernel_text(pc + 1) || is_kernel_inittext(pc + 1)) ) ... these checks anyway? And btw, why the "+ 1" in both function arguments? > + { > + printk("Something wrong with PC: 0x%lx\n", pc); Nit: %#lx please in situations like this. > + die(); > + } > + > + cpu_regs->sepc += GET_INSN_LENGTH(*(uint16_t *)pc); > + return; This isn't needed, is it? You'd return anyway by ... > + } > + > + break; .... going through here to ... > + default: > + do_unexpected_trap(cpu_regs); > + } > } ... here. Two further nits for the default case: Please have a break statement there as well, and please have a blank line immediately up from it. Jan
On Mon, 2024-07-22 at 13:02 +0200, Jan Beulich wrote: > On 12.07.2024 18:18, Oleksii Kurochko wrote: > > To have working BUG(), WARN(), ASSERT, run_in_exception_handler() > > it is needed to enable GENERIC_BUG_FRAME. > > > > Also, <xen/lib.h> is needed to be included for the reason that > > panic() and > > printk() are used in common/bug.c and RISC-V fails if it is not > > included > > with the following errors: > > common/bug.c:69:9: error: implicit declaration of function > > 'printk' > > [-Werror=implicit-function-declaration] > > 69 | printk("Xen WARN at %s%s:%d\n", prefix, > > filename, > > lineno); > > | ^~~~~~ > > common/bug.c:77:9: error: implicit declaration of function > > 'panic' > > [-Werror=implicit-function-declaration] > > 77 | panic("Xen BUG at %s%s:%d\n", prefix, filename, > > lineno); > > I don't think the diagnostics themselves are needed here. > > > Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com> > > --- > > Changes in V10: > > - put 'select GENERIC_BUG_FRAME' in "Config RISCV". > > - rework do_trap() to not fetch an instruction in case when the > > cause of trap > > is BUG_insn. > > It's BUG_insn here, but then ... > > > @@ -103,7 +104,29 @@ static void do_unexpected_trap(const struct > > cpu_user_regs *regs) > > > > void do_trap(struct cpu_user_regs *cpu_regs) > > { > > - do_unexpected_trap(cpu_regs); > > + register_t pc = cpu_regs->sepc; > > + unsigned long cause = csr_read(CSR_SCAUSE); > > + > > + switch ( cause ) > > + { > > + case CAUSE_BREAKPOINT: > > ... BREAKPOINT here? Generally I'd deem something named "breakpoint" > as > debugging related (and hence continuable). I'd have expected > CAUSE_ILLEGAL_INSTRUCTION here, but likely I'm missing something. Agree, that is is confusing, but BUG_insn is defined as ebreak instruction ( Linux kernel uses also ebreak ) and it generates CAUSE_BREAKPOINT. > > > + if ( do_bug_frame(cpu_regs, pc) >= 0 ) > > + { > > + if ( !pc || > > In how far does this really need special casing? Isn't that case > covered by > > > + !(is_kernel_text(pc + 1) || is_kernel_inittext(pc > > + 1)) ) > > ... these checks anyway? Good point. We could drop it. > And btw, why the "+ 1" in both function arguments? There is no need for them anymore, just missed to drop +1. ~ Oleksii > > > + { > > + printk("Something wrong with PC: 0x%lx\n", pc); > > Nit: %#lx please in situations like this. > > > + die(); > > + } > > + > > + cpu_regs->sepc += GET_INSN_LENGTH(*(uint16_t *)pc); > > + return; > > This isn't needed, is it? You'd return anyway by ... > > > + } > > + > > + break; > > .... going through here to ... > > > + default: > > + do_unexpected_trap(cpu_regs); > > + } > > } > > ... here. > > Two further nits for the default case: Please have a break statement > there as well, and please have a blank line immediately up from it. > > Jan
On 22.07.2024 16:09, Oleksii wrote: > On Mon, 2024-07-22 at 13:02 +0200, Jan Beulich wrote: >> On 12.07.2024 18:18, Oleksii Kurochko wrote: >>> --- >>> Changes in V10: >>> - put 'select GENERIC_BUG_FRAME' in "Config RISCV". >>> - rework do_trap() to not fetch an instruction in case when the >>> cause of trap >>> is BUG_insn. >> >> It's BUG_insn here, but then ... >> >>> @@ -103,7 +104,29 @@ static void do_unexpected_trap(const struct >>> cpu_user_regs *regs) >>> >>> void do_trap(struct cpu_user_regs *cpu_regs) >>> { >>> - do_unexpected_trap(cpu_regs); >>> + register_t pc = cpu_regs->sepc; >>> + unsigned long cause = csr_read(CSR_SCAUSE); >>> + >>> + switch ( cause ) >>> + { >>> + case CAUSE_BREAKPOINT: >> >> ... BREAKPOINT here? Generally I'd deem something named "breakpoint" >> as >> debugging related (and hence continuable). I'd have expected >> CAUSE_ILLEGAL_INSTRUCTION here, but likely I'm missing something. > Agree, that is is confusing, but BUG_insn is defined as ebreak > instruction ( Linux kernel uses also ebreak ) and it generates > CAUSE_BREAKPOINT. I'm curious: How do you / does a debugger tell a breakpoint set on such an EBREAK insn (e.g. as a result of a use of WARN_ON()) from the original, unmodified insn? If there's a breakpoint, you want to forward to the debugger. Whereas if there's no breakpoint, you want to process the WARN_ON() normally. Jan
On Mon, 2024-07-22 at 17:32 +0200, Jan Beulich wrote: > On 22.07.2024 16:09, Oleksii wrote: > > On Mon, 2024-07-22 at 13:02 +0200, Jan Beulich wrote: > > > On 12.07.2024 18:18, Oleksii Kurochko wrote: > > > > --- > > > > Changes in V10: > > > > - put 'select GENERIC_BUG_FRAME' in "Config RISCV". > > > > - rework do_trap() to not fetch an instruction in case when > > > > the > > > > cause of trap > > > > is BUG_insn. > > > > > > It's BUG_insn here, but then ... > > > > > > > @@ -103,7 +104,29 @@ static void do_unexpected_trap(const > > > > struct > > > > cpu_user_regs *regs) > > > > > > > > void do_trap(struct cpu_user_regs *cpu_regs) > > > > { > > > > - do_unexpected_trap(cpu_regs); > > > > + register_t pc = cpu_regs->sepc; > > > > + unsigned long cause = csr_read(CSR_SCAUSE); > > > > + > > > > + switch ( cause ) > > > > + { > > > > + case CAUSE_BREAKPOINT: > > > > > > ... BREAKPOINT here? Generally I'd deem something named > > > "breakpoint" > > > as > > > debugging related (and hence continuable). I'd have expected > > > CAUSE_ILLEGAL_INSTRUCTION here, but likely I'm missing something. > > Agree, that is is confusing, but BUG_insn is defined as ebreak > > instruction ( Linux kernel uses also ebreak ) and it generates > > CAUSE_BREAKPOINT. > > I'm curious: How do you / does a debugger tell a breakpoint set on > such an EBREAK insn (e.g. as a result of a use of WARN_ON()) from > the original, unmodified insn? If there's a breakpoint, you want > to forward to the debugger. Whereas if there's no breakpoint, you > want to process the WARN_ON() normally. I don't know details of debug spec but AFAIU ebreak triggers a debug trap, which starts in debug mode and is then filtered by every mode as it goes towards user-mode. So first GDB will handle this debug trap and will check if this ebreak was set by him or not. ~ Oleksii
diff --git a/xen/arch/riscv/Kconfig b/xen/arch/riscv/Kconfig index b4b354a778..f531e96657 100644 --- a/xen/arch/riscv/Kconfig +++ b/xen/arch/riscv/Kconfig @@ -1,6 +1,7 @@ config RISCV def_bool y select FUNCTION_ALIGNMENT_16B + select GENERIC_BUG_FRAME config RISCV_64 def_bool y diff --git a/xen/arch/riscv/traps.c b/xen/arch/riscv/traps.c index cb18b30ff2..e39603dc95 100644 --- a/xen/arch/riscv/traps.c +++ b/xen/arch/riscv/traps.c @@ -5,6 +5,7 @@ * RISC-V Trap handlers */ +#include <xen/bug.h> #include <xen/lib.h> #include <xen/sched.h> @@ -103,7 +104,29 @@ static void do_unexpected_trap(const struct cpu_user_regs *regs) void do_trap(struct cpu_user_regs *cpu_regs) { - do_unexpected_trap(cpu_regs); + register_t pc = cpu_regs->sepc; + unsigned long cause = csr_read(CSR_SCAUSE); + + switch ( cause ) + { + case CAUSE_BREAKPOINT: + if ( do_bug_frame(cpu_regs, pc) >= 0 ) + { + if ( !pc || + !(is_kernel_text(pc + 1) || is_kernel_inittext(pc + 1)) ) + { + printk("Something wrong with PC: 0x%lx\n", pc); + die(); + } + + cpu_regs->sepc += GET_INSN_LENGTH(*(uint16_t *)pc); + return; + } + + break; + default: + do_unexpected_trap(cpu_regs); + } } void vcpu_show_execution_state(struct vcpu *v) diff --git a/xen/common/bug.c b/xen/common/bug.c index b7c5d8fd4d..75cb35fcfa 100644 --- a/xen/common/bug.c +++ b/xen/common/bug.c @@ -1,6 +1,7 @@ #include <xen/bug.h> #include <xen/errno.h> #include <xen/kernel.h> +#include <xen/lib.h> #include <xen/livepatch.h> #include <xen/string.h> #include <xen/types.h>
To have working BUG(), WARN(), ASSERT, run_in_exception_handler() it is needed to enable GENERIC_BUG_FRAME. Also, <xen/lib.h> is needed to be included for the reason that panic() and printk() are used in common/bug.c and RISC-V fails if it is not included with the following errors: common/bug.c:69:9: error: implicit declaration of function 'printk' [-Werror=implicit-function-declaration] 69 | printk("Xen WARN at %s%s:%d\n", prefix, filename, lineno); | ^~~~~~ common/bug.c:77:9: error: implicit declaration of function 'panic' [-Werror=implicit-function-declaration] 77 | panic("Xen BUG at %s%s:%d\n", prefix, filename, lineno); Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com> --- Changes in V10: - put 'select GENERIC_BUG_FRAME' in "Config RISCV". - rework do_trap() to not fetch an instruction in case when the cause of trap is BUG_insn. - drop read_instr() and is_valid_bug_insn(). - update the commit message. --- Changes in V9: - Rebase on the top of current staging. - use GENERIC_BUG_FRAME as now we have common code available. - add xen/lib.h to bug.c to fix a compilation error around printk. - update the commit message. - update the code of read_instr() in traps.c - fold two-s if into 1 in do_trap. --- Changes in V8: - remove Pointless initializer of id. - make bug_frames[] array constant. - remove cast_to_bug_frame(addr). - rename is_valig_bugaddr to is_valid_bug_insn(). - add check that read_instr is used only on xen code - update the commit message. --- Changes in V7: - move to this patch the definition of cast_to_bug_frame() from the previous patch. - update the comment in bug.h. - update the comment above do_bug_frame(). - fix code style. - add comment to read_instr func. - add space for bug_frames in lds.S. --- Changes in V6: - Avoid LINK_TO_LOAD() as bug.h functionality expected to be used after MMU is enabled. - Change early_printk() to printk() --- Changes in V5: - Remove "#include <xen/types.h>" from <asm/bug.h> as there is no any need in it anymore - Update macros GET_INSN_LENGTH: remove UL and 'unsigned int len;' from it - Remove " include <xen/bug.h>" from risc/setup.c. it is not needed in the current version of the patch - change an argument type from vaddr_t to uint32_t for is_valid_bugaddr and introduce read_instr() to read instruction properly as the length of qinstruction can be either 32 or 16 bits. - Code style fixes - update the comments before do_bug_frame() in riscv/trap.c - Refactor is_valid_bugaddr() function. - introduce macros cast_to_bug_frame(addr) to hide casts. - use LINK_TO_LOAD() for addresses which are linker time relative. --- Changes in V4: - Updates in RISC-V's <asm/bug.h>: * Add explanatory comment about why there is only defined for 32-bits length instructions and 16/32-bits BUG_INSN_{16,32}. * Change 'unsigned long' to 'unsigned int' inside GET_INSN_LENGTH(). * Update declaration of is_valid_bugaddr(): switch return type from int to bool and the argument from 'unsigned int' to 'vaddr'. - Updates in RISC-V's traps.c: * replace /xen and /asm includes * update definition of is_valid_bugaddr():switch return type from int to bool and the argument from 'unsigned int' to 'vaddr'. Code style inside function was updated too. * do_bug_frame() refactoring: * local variables start and bug became 'const struct bug_frame' * bug_frames[] array became 'static const struct bug_frame[] = ...' * remove all casts * remove unneeded comments and add an explanatory comment that the do_bug_frame() will be switched to a generic one. * do_trap() refactoring: * read 16-bits value instead of 32-bits as compressed instruction can be used and it might happen than only 16-bits may be accessible. * code style updates * re-use instr variable instead of re-reading instruction. - Updates in setup.c: * add blank line between xen/ and asm/ includes. --- Changes in V3: - Rebase the patch "xen/riscv: introduce an implementation of macros from <asm/bug.h>" on top of patch series [introduce generic implementation of macros from bug.h] --- Changes in V2: - Remove __ in define namings - Update run_in_exception_handler() with register void *fn_ asm(__stringify(BUG_FN_REG)) = (fn); - Remove bug_instr_t type and change it's usage to uint32_t --- xen/arch/riscv/Kconfig | 1 + xen/arch/riscv/traps.c | 25 ++++++++++++++++++++++++- xen/common/bug.c | 1 + 3 files changed, 26 insertions(+), 1 deletion(-)