Add support for a semihosting fallback on 32-bit ARM. The assembly is
lightly adapted from the irq return code, except there is no offset
since lr already points to the correct instruction. The C side is mostly
like ARM64, except we have fewer cases to deal with.
Signed-off-by: Sean Anderson <sean.ander...@seco.com>
---
arch/arm/lib/interrupts.c | 31 +++++++++++++++++++++++++++++++
arch/arm/lib/vectors.S | 7 +++++++
lib/Kconfig | 4 ++--
3 files changed, 40 insertions(+), 2 deletions(-)
diff --git a/arch/arm/lib/interrupts.c b/arch/arm/lib/interrupts.c
index 6dc27d1d589..9961472f69f 100644
--- a/arch/arm/lib/interrupts.c
+++ b/arch/arm/lib/interrupts.c
@@ -22,6 +22,7 @@
#include <cpu_func.h>
#include <efi_loader.h>
#include <irq_func.h>
+#include <semihosting.h>
#include <asm/global_data.h>
#include <asm/proc-armv/ptrace.h>
#include <asm/ptrace.h>
@@ -135,6 +136,32 @@ static inline void fixup_pc(struct pt_regs *regs, int
offset)
regs->ARM_pc = pc | (regs->ARM_pc & PCMASK);
}
+/*
+ * Try to "emulate" a semihosting call in the event that we don't have a
+ * debugger attached.
+ */
+static bool smh_emulate_trap(struct pt_regs *regs)
+{
+ if (regs->ARM_cpsr & T_BIT) {
+ u16 *insn = (u16 *)(regs->ARM_pc - 2);
+
+ if (*insn != SMH_T32_SVC)
+ return false;
+ } else {
+ u32 *insn = (u32 *)(regs->ARM_pc - 4);
+
+ if (*insn != SMH_A32_SVC)
+ return false;
+ }
+
+ /* Avoid future semihosting calls */
+ disable_semihosting();
+
+ /* Just pretend the call failed */
+ regs->ARM_r0 = -1;
+ return true;
+}
+
void do_undefined_instruction (struct pt_regs *pt_regs)
{
efi_restore_gd();
@@ -147,6 +174,10 @@ void do_undefined_instruction (struct pt_regs *pt_regs)
void do_software_interrupt (struct pt_regs *pt_regs)
{
+ if (CONFIG_IS_ENABLED(SEMIHOSTING_FALLBACK) &&
+ smh_emulate_trap(pt_regs))
+ return;
+
efi_restore_gd();
printf ("software interrupt\n");
fixup_pc(pt_regs, -4);
diff --git a/arch/arm/lib/vectors.S b/arch/arm/lib/vectors.S
index fe8ca403ac9..843f9b9c281 100644
--- a/arch/arm/lib/vectors.S
+++ b/arch/arm/lib/vectors.S
@@ -275,6 +275,13 @@ software_interrupt:
get_bad_stack_swi
bad_save_user_regs
bl do_software_interrupt
+#if CONFIG_IS_ENABLED(SEMIHOSTING_FALLBACK)
+ ldmia sp, {r0 - lr}^ @ Calling r0 - lr
+ mov r0, r0
+ ldr lr, [sp, #S_PC] @ Get PC
+ add sp, sp, #S_FRAME_SIZE
+ movs pc, lr @ return & move spsr_svc into cpsr
+#endif
.align 5
prefetch_abort:
diff --git a/lib/Kconfig b/lib/Kconfig
index f6ca559897e..3cabb07bfd6 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -93,7 +93,7 @@ config SEMIHOSTING
config SEMIHOSTING_FALLBACK
bool "Recover gracefully when semihosting fails"
- depends on SEMIHOSTING && (ARM64 || RISCV)
+ depends on SEMIHOSTING
default y
help
Normally, if U-Boot makes a semihosting call and no debugger is
@@ -116,7 +116,7 @@ config SPL_SEMIHOSTING
config SPL_SEMIHOSTING_FALLBACK
bool "Recover gracefully when semihosting fails in SPL"
- depends on SPL_SEMIHOSTING && (ARM64 || RISCV)
+ depends on SPL_SEMIHOSTING
select ARMV8_SPL_EXCEPTION_VECTORS if ARM64
default y
help
--
2.35.1.1320.gc452695387.dirty
