arm baremetal: SVC explain where the imm16 can be retrieved

Use upper case hex literals on all PRIXnn. .gitignore /out.docker
2025-08-15 22:36:35 +00:00 · 2019-07-16 00:00:01 +00:00
parent b1bfd46efe
commit b38e2b0da9
10 changed files with 140 additions and 75 deletions
--- a/.gitignore
+++ b/.gitignore
@ -1,5 +1,7 @@
 # Important directories.
 /out
+# https://github.com/cirosantilli/linux-kernel-module-cheat#docker
+/out.docker
 /data

 # Temporary files.
--- a/README.adoc
+++ b/README.adoc
@ -10148,7 +10148,7 @@ Behaviour breakdown:
 So we take a performance measurement approach instead:

 ....
-./gem5-bench-cache --arch aarch64
+./gem5-bench-cache -- --arch aarch64
 cat "$(./getvar --arch aarch64 run_dir)/bench-cache.txt"
 ....

@ -14672,26 +14672,29 @@ Sources:
 Sample output for the C one:

 ....
-daif 0x3c0
-spsel 0x1
-vbar_el1 0x40000800
+DAIF 0x3C0
+SPSEL 0x1
+VBAR_EL1 0x40000800
+after_svc 0x4000209c
 lkmc_vector_trap_handler
 exc_type 0x11
 exc_type is LKMC_VECTOR_SYNC_SPX
-ESR 0x56000042
-SP 0x4200bba8
-ELR 0x40002470
-SPSR 0x600003c5
+ESR 0x5600ABCD
+ESR.EC 0x15
+ESR.EC.ISS.imm16 0xABCD
+SP 0x4200C510
+ELR 0x4000209C
+SPSR 0x600003C5
 x0 0x0
 x1 0x1
-x2 0x14
-x3 0x14
-x4 0x40008390
-x5 0xfffffff8
-x6 0x4200ba28
-x7 0x0
-x8 0x0
-x9 0x13
+x2 0x15
+x3 0x15
+x4 0x4000A178
+x5 0xFFFFFFF6
+x6 0x4200C390
+x7 0x78
+x8 0x1
+x9 0x14
 x10 0x0
 x11 0x0
 x12 0x0
@ -14711,11 +14714,36 @@ x25 0x0
 x26 0x0
 x27 0x0
 x28 0x0
-x29 0x4200bba8
-x30 0x4000246c
+x29 0x4200C510
+x30 0x40002064
 ....

-Both QEMU and gem5 are able to trace interrupts in addition to instructions, and it is instructive to enable both and have a look at the traces:
+The C code does an:
+
+....
+svc 0xABCD
+....
+
+and the value 0xABCD appears at the bottom of <<arm-esr-register>>:
+
+....
+ESR 0x5600ABCD
+ESR.EC 0x15
+ESR.EC.ISS.imm16 0xABCD
+....
+
+The other important register is the <<arm-elr-register>>, which contains the return address after the exception.
+
+From the output, we can see that it matches the value as obtained by taking the address of a label placed just after the SVC:
+
+....
+after_svc 0x4000209c
+ELR 0x4000209C
+....
+
+Both QEMU and gem5 are able to trace interrupts in addition to instructions, and it is instructive to enable both and have a look at the traces.
+
+With <<qemu-d-tracing>>:

 ....
 ./run \
@ -14725,7 +14753,7 @@ Both QEMU and gem5 are able to trace interrupts in addition to instructions, and
 ;
 ....

-contains:
+the output contains:

 ....
 ----------------
@ -14742,7 +14770,7 @@ IN:
 0x40000a00:  14000225  b        #0x40001294
 ....

-and:
+And with <<gem5-tracing>>:

 ....
 ./run \
@ -14753,7 +14781,7 @@ and:
 ;
 ....

-contains:
+the output contains:

 ....
   4000: system.cpu A0 T0 : @main+8    :   svc   #0x0               : IntAlu :   flags=(IsSerializeAfter|IsNonSpeculative|IsSyscall)
@ -14818,6 +14846,20 @@ Bibliography:
 * https://stackoverflow.com/questions/44991264/armv8-exception-vectors-and-handling
 * https://stackoverflow.com/questions/44198483/arm-timers-and-interrupts

+===== ARM ESR register
+
+Exception Syndrome Register.
+
+See example at: <<arm-svc-instruction>>
+
+Documentation: <<armarm8-db>> D12.2.36 "ESR_EL1, Exception Syndrome Register (EL1)".
+
+===== ARM ELR register
+
+Exception Link Register.
+
+See example at: <<arm-svc-instruction>>
+
 ==== ARM multicore

 ....
--- a/baremetal/arch/aarch64/svc.c
+++ b/baremetal/arch/aarch64/svc.c
@ -11,55 +11,68 @@ int myvar = 0;

 void lkmc_vector_trap_handler(LkmcVectorExceptionFrame *exception) {
    puts("lkmc_vector_trap_handler");
-    printf("exc_type 0x%" PRIx64 "\n", exception->exc_type);
+    printf("exc_type 0x%" PRIX64 "\n", exception->exc_type);
    if (exception->exc_type == LKMC_VECTOR_SYNC_SPX) {
        puts("exc_type is LKMC_VECTOR_SYNC_SPX");
    }
-    printf("ESR 0x%" PRIx64 "\n", exception->exc_esr);
-    printf("SP 0x%" PRIx64 "\n", exception->exc_sp);
-    printf("ELR 0x%" PRIx64 "\n", exception->exc_elr);
-    printf("SPSR 0x%" PRIx64 "\n", exception->exc_spsr);
-    printf("x0 0x%" PRIx64 "\n", exception->x0);
-    printf("x1 0x%" PRIx64 "\n", exception->x1);
-    printf("x2 0x%" PRIx64 "\n", exception->x2);
-    printf("x3 0x%" PRIx64 "\n", exception->x3);
-    printf("x4 0x%" PRIx64 "\n", exception->x4);
-    printf("x5 0x%" PRIx64 "\n", exception->x5);
-    printf("x6 0x%" PRIx64 "\n", exception->x6);
-    printf("x7 0x%" PRIx64 "\n", exception->x7);
-    printf("x8 0x%" PRIx64 "\n", exception->x8);
-    printf("x9 0x%" PRIx64 "\n", exception->x9);
-    printf("x10 0x%" PRIx64 "\n", exception->x10);
-    printf("x11 0x%" PRIx64 "\n", exception->x11);
-    printf("x12 0x%" PRIx64 "\n", exception->x12);
-    printf("x13 0x%" PRIx64 "\n", exception->x13);
-    printf("x14 0x%" PRIx64 "\n", exception->x14);
-    printf("x15 0x%" PRIx64 "\n", exception->x15);
-    printf("x16 0x%" PRIx64 "\n", exception->x16);
-    printf("x17 0x%" PRIx64 "\n", exception->x17);
-    printf("x18 0x%" PRIx64 "\n", exception->x18);
-    printf("x19 0x%" PRIx64 "\n", exception->x19);
-    printf("x20 0x%" PRIx64 "\n", exception->x20);
-    printf("x21 0x%" PRIx64 "\n", exception->x21);
-    printf("x22 0x%" PRIx64 "\n", exception->x22);
-    printf("x23 0x%" PRIx64 "\n", exception->x23);
-    printf("x24 0x%" PRIx64 "\n", exception->x24);
-    printf("x25 0x%" PRIx64 "\n", exception->x25);
-    printf("x26 0x%" PRIx64 "\n", exception->x26);
-    printf("x27 0x%" PRIx64 "\n", exception->x27);
-    printf("x28 0x%" PRIx64 "\n", exception->x28);
-    printf("x29 0x%" PRIx64 "\n", exception->x29);
-    printf("x30 0x%" PRIx64 "\n", exception->x30);
+    printf("ESR 0x%" PRIX64 "\n", exception->exc_esr);
+    uint64_t esr_ec = (exception->exc_esr >> 26) & 0x3F;
+    uint64_t iss = exception->exc_esr & 0xFFFFFF;
+    printf("ESR.EC 0x%" PRIX64 "\n", esr_ec);
+    if (
+        esr_ec == LKMC_ESR_EC_SVC_AARCH32 ||
+        esr_ec == LKMC_ESR_EC_SVC_AARCH64
+    ) {
+        printf("ESR.EC.ISS.imm16 0x%" PRIX64 "\n", iss & 0xFFFF);
+    }
+    printf("SP 0x%" PRIX64 "\n", exception->exc_sp);
+    printf("ELR 0x%" PRIX64 "\n", exception->exc_elr);
+    printf("SPSR 0x%" PRIX64 "\n", exception->exc_spsr);
+    printf("x0 0x%" PRIX64 "\n", exception->x0);
+    printf("x1 0x%" PRIX64 "\n", exception->x1);
+    printf("x2 0x%" PRIX64 "\n", exception->x2);
+    printf("x3 0x%" PRIX64 "\n", exception->x3);
+    printf("x4 0x%" PRIX64 "\n", exception->x4);
+    printf("x5 0x%" PRIX64 "\n", exception->x5);
+    printf("x6 0x%" PRIX64 "\n", exception->x6);
+    printf("x7 0x%" PRIX64 "\n", exception->x7);
+    printf("x8 0x%" PRIX64 "\n", exception->x8);
+    printf("x9 0x%" PRIX64 "\n", exception->x9);
+    printf("x10 0x%" PRIX64 "\n", exception->x10);
+    printf("x11 0x%" PRIX64 "\n", exception->x11);
+    printf("x12 0x%" PRIX64 "\n", exception->x12);
+    printf("x13 0x%" PRIX64 "\n", exception->x13);
+    printf("x14 0x%" PRIX64 "\n", exception->x14);
+    printf("x15 0x%" PRIX64 "\n", exception->x15);
+    printf("x16 0x%" PRIX64 "\n", exception->x16);
+    printf("x17 0x%" PRIX64 "\n", exception->x17);
+    printf("x18 0x%" PRIX64 "\n", exception->x18);
+    printf("x19 0x%" PRIX64 "\n", exception->x19);
+    printf("x20 0x%" PRIX64 "\n", exception->x20);
+    printf("x21 0x%" PRIX64 "\n", exception->x21);
+    printf("x22 0x%" PRIX64 "\n", exception->x22);
+    printf("x23 0x%" PRIX64 "\n", exception->x23);
+    printf("x24 0x%" PRIX64 "\n", exception->x24);
+    printf("x25 0x%" PRIX64 "\n", exception->x25);
+    printf("x26 0x%" PRIX64 "\n", exception->x26);
+    printf("x27 0x%" PRIX64 "\n", exception->x27);
+    printf("x28 0x%" PRIX64 "\n", exception->x28);
+    printf("x29 0x%" PRIX64 "\n", exception->x29);
+    printf("x30 0x%" PRIX64 "\n", exception->x30);
    myvar = 1;
 }

 int main(void) {
    /* View initial relevant register values. */
-    printf("daif 0x%" PRIx32 "\n", lkmc_sysreg_daif_read());
-    printf("spsel 0x%" PRIx32 "\n", lkmc_sysreg_spsel_read());
-    printf("vbar_el1 0x%" PRIx64 "\n", lkmc_sysreg_vbar_el1_read());
+    printf("DAIF 0x%" PRIX32 "\n", lkmc_sysreg_daif_read());
+    printf("SPSEL 0x%" PRIX32 "\n", lkmc_sysreg_spsel_read());
+    printf("VBAR_EL1 0x%" PRIX64 "\n", lkmc_sysreg_vbar_el1_read());
+    /* https://stackoverflow.com/questions/1777990/is-it-possible-to-store-the-address-of-a-label-in-a-variable-and-use-goto-to-jum */
+    printf("after_svc %p\n", &&after_svc);
    assert(myvar == 0);
-    LKMC_SVC(0x42);
+    /* Max 16-bits. */
+    LKMC_SVC(0xABCD);
+after_svc:
    assert(myvar == 1);
    return 0;
 }
--- a/baremetal/arch/aarch64/svc_asm.S
+++ b/baremetal/arch/aarch64/svc_asm.S
@ -5,7 +5,7 @@
 .global main
 main:
    /* Do the svc. */
-    svc 0
+    svc 0xABCD

    /* Confirm that svc was called and modified myvar. */
    ldr x0, myvar
--- a/baremetal/arch/aarch64/timer.c
+++ b/baremetal/arch/aarch64/timer.c
@ -5,7 +5,7 @@
 #include <lkmc/gicv3.h>

 void lkmc_vector_trap_handler(LkmcVectorExceptionFrame *exception __attribute__((unused))) {
-    printf("CNTVCT_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntvct_el0_read());
+    printf("CNTVCT_EL0 0x%" PRIX64 "\n", lkmc_sysreg_cntvct_el0_read());
 }

 #define CNTV_CTL_ENABLE  (1 << 0) /* Enables the timer */ 
@ -30,14 +30,14 @@ void enable_irq(void) {

 int main(void) {
    /* Initial state. */
-    printf("CNTV_CTL_EL0 0x%" PRIx32 "\n", lkmc_sysreg_cntv_ctl_el0_read());
-    printf("CNTFRQ_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntfrq_el0_read());
-    printf("CNTV_CVAL_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntv_cval_el0_read());
+    printf("CNTV_CTL_EL0 0x%" PRIX32 "\n", lkmc_sysreg_cntv_ctl_el0_read());
+    printf("CNTFRQ_EL0 0x%" PRIX64 "\n", lkmc_sysreg_cntfrq_el0_read());
+    printf("CNTV_CVAL_EL0 0x%" PRIX64 "\n", lkmc_sysreg_cntv_cval_el0_read());

    /* Get the counter value many times to watch the time pass. */
-    printf("CNTVCT_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntvct_el0_read());
-    printf("CNTVCT_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntvct_el0_read());
-    printf("CNTVCT_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntvct_el0_read());
+    printf("CNTVCT_EL0 0x%" PRIX64 "\n", lkmc_sysreg_cntvct_el0_read());
+    printf("CNTVCT_EL0 0x%" PRIX64 "\n", lkmc_sysreg_cntvct_el0_read());
+    printf("CNTVCT_EL0 0x%" PRIX64 "\n", lkmc_sysreg_cntvct_el0_read());

    /**/
    gic_v3_initialize();
@ -66,7 +66,7 @@ int main(void) {
    /* TODO crashes gem5. */
    puts("cntfrq_el0 = 1");
    lkmc_sysreg_cntfrq_el0_write(1);
-    printf("cntfrq_el0 0x%" PRIx64 "\n", lkmc_sysreg_cntfrq_el0_read());
+    printf("cntfrq_el0 0x%" PRIX64 "\n", lkmc_sysreg_cntfrq_el0_read());
 #endif

    return 0;
--- a/baremetal/lib/aarch64.S
+++ b/baremetal/lib/aarch64.S
@ -28,7 +28,10 @@ lkmc_start:

 LKMC_VECTOR_TABLE

-/* Default trap handler. */
+/* Default handler for exceptions. This is called after some basic
+ * setup done on the initial handler. Since this is a weak symbol,
+ * you can redefine it in your own example, and your definition
+ * will take precedence. */
 LKMC_WEAK(lkmc_vector_trap_handler)
    ldr x0, =lkmc_vector_trap_handler_error_message
    bl puts
--- a/2
+++ b/2
@ -67,7 +67,7 @@ bench-all() (

 if "$generate_checkpoints"; then
  # Create the checkpoints after the kernel boot.
-  cpt_cmd="-E '/gem5.sh'"
+  cpt_cmd="--eval './gem5.sh'"
  # RESTORE_INVESTIGATION
  ## 5
  #./eeval "$cmd $cpt_cmd -- $cache_large --cpu-type=HPI"
--- a/lkmc/aarch64.h
+++ b/lkmc/aarch64.h
@ -92,14 +92,18 @@ main_after_prologue: \

 #define LKMC_VECTOR_EXC_FRAME_SIZE      (288) /* sizeof(lkmc_vector_exception_frame)             */
 #define LKMC_VECTOR_EXC_EXC_TYPE_OFFSET (0)   /* offsetof(lkmc_vector_exception_frame, exc_type) */
-#define LKMC_VECTOR_EXC_EXC_ESR_OFFSE   (8)   /* offsetof(lkmc_vector_exception_frame, exc_esr)  */
+#define LKMC_VECTOR_EXC_EXC_ESR_OFFSET  (8)   /* offsetof(lkmc_vector_exception_frame, exc_esr)  */
 #define LKMC_VECTOR_EXC_EXC_SP_OFFSET   (16)  /* offsetof(lkmc_vector_exception_frame, exc_sp)   */
 #define LKMC_VECTOR_EXC_EXC_ELR_OFFSET  (24)  /* offsetof(lkmc_vector_exception_frame, exc_elr)  */
 #define LKMC_VECTOR_EXC_EXC_SPSR_OFFSET (32)  /* offsetof(lkmc_vector_exception_frame, exc_spsr) */

+#define LKMC_ESR_EC_SVC_AARCH32 (0x11)
+#define LKMC_ESR_EC_SVC_AARCH64 (0x15)
+
 #define LKMC_VECTOR_FUNC_ALIGN .align 2
 #define LKMC_VECTOR_SYMBOL_PREFIX lkmc_vector_

+/* Push several registers on the stack to match LkmcVectorExceptionFrame. */
 #define LKMC_VECTOR_BUILD_TRAPFRAME(exc_type) \
    stp x29, x30, [sp, -16]!; \
    stp x27, x28, [sp, -16]!; \
--- a/path_properties.py
+++ b/path_properties.py
@ -310,6 +310,7 @@ path_properties_tuples = (
                                ),
                                'return1.S': {'exit_status': 1},
                                'semihost_exit.S': {'requires_semihosting': True},
+                                'svc.c': {'cc_pedantic': False},
                                'timer.c': {'skip_run_unclassified': True},
                            },
                        )
--- a/userland/linux/rand_check.c
+++ b/userland/linux/rand_check.c
@ -36,6 +36,6 @@ int main(__attribute__((unused)) int argc, char **argv) {
    /* /dev/urandom */
    fp = fopen("/dev/urandom", "rb");
    fread(&uint64, sizeof(uint64), 1, fp);
-    printf("/dev/urandom = %" PRIx64 "\n", uint64);
+    printf("/dev/urandom = %" PRIX64 "\n", uint64);
    fclose(fp);
 }