v5: simplify JBSMATCH_OPCODE implementation

R=1 is not usable due to having *run* time determined encoding length.

We'll reuse this for jmp condition negation in an upcoming change.

After this:
 text	   data	    bss	    dec	    hex	filename
   3892	      0	      0	   3892	    f34	apf_interpreter.arm.o
   text	   data	    bss	    dec	    hex	filename
   4924	      0	      0	   4924	   133c	apf_interpreter.x86.o

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I61ad0f93ae649765e4ab04e65a0a56f2742583e7

2 files changed, 12 insertions, 18 deletions

diff --git a/v5/apf_interpreter.c b/v5/apf_interpreter.c
index f3b6726..7e31b4d 100644
--- a/v5/apf_interpreter.c
+++ b/v5/apf_interpreter.c
@@ -594,7 +594,7 @@ extern void APF_TRACE_HOOK(u32 pc, const u32* regs, const u8* program,
 #define ENFORCE_UNSIGNED(c) ((c)==(u32)(c))
 
 u32 apf_version(void) {
-    return 20240312;
+    return 20240313;
 }
 
 typedef struct {
@@ -788,19 +788,16 @@ static int do_apf_run(apf_context* ctx) {
               break;
           }
           case JBSMATCH_OPCODE: {
+              /* with len_field == 0, we have imm == cmp_imm == 0 and thus a jmp +0, ie. a no-op */
+              if (len_field == 0) break;
               /* Load second immediate field. */
-              u32 cmp_imm = 0;
-              if (reg_num == 1) {
-                  cmp_imm = ctx->R[1];
-              } else if (len_field != 0) {
-                  u32 cmp_imm_len = 1 << (len_field - 1);
-                  cmp_imm = decode_imm(ctx, cmp_imm_len); /* 2nd imm, at worst 8 bytes past prog_len */
-              }
+              u32 cmp_imm_len = 1 << (len_field - 1);
+              u32 cmp_imm = decode_imm(ctx, cmp_imm_len); /* 2nd imm, at worst 4 bytes past prog_len */
               /* cmp_imm is size in bytes of data to compare. */
               /* pc is offset of program bytes to compare. */
               /* imm is jump target offset. */
               /* REG is offset of packet bytes to compare. */
-              if (len_field > 2) return PASS_PACKET; /* guarantees cmp_imm <= 0xFFFF */
+              if (cmp_imm > 0xFFFF) return PASS_PACKET;
               /* pc < program_len < ram_len < 2GiB, thus pc + cmp_imm cannot wrap */
               if (!IN_RAM_BOUNDS(ctx->pc + cmp_imm - 1)) return PASS_PACKET;
               ASSERT_IN_PACKET_BOUNDS(REG);
diff --git a/v5/apf_interpreter_source.c b/v5/apf_interpreter_source.c
index 5b8b4cc..67d11ec 100644
--- a/v5/apf_interpreter_source.c
+++ b/v5/apf_interpreter_source.c
@@ -61,7 +61,7 @@ extern void APF_TRACE_HOOK(u32 pc, const u32* regs, const u8* program,
 #define ENFORCE_UNSIGNED(c) ((c)==(u32)(c))
 
 u32 apf_version(void) {
-    return 20240312;
+    return 20240313;
 }
 
 typedef struct {
@@ -255,19 +255,16 @@ static int do_apf_run(apf_context* ctx) {
               break;
           }
           case JBSMATCH_OPCODE: {
+              // with len_field == 0, we have imm == cmp_imm == 0 and thus a jmp +0, ie. a no-op
+              if (len_field == 0) break;
               // Load second immediate field.
-              u32 cmp_imm = 0;
-              if (reg_num == 1) {
-                  cmp_imm = ctx->R[1];
-              } else if (len_field != 0) {
-                  u32 cmp_imm_len = 1 << (len_field - 1);
-                  cmp_imm = decode_imm(ctx, cmp_imm_len); // 2nd imm, at worst 8 bytes past prog_len
-              }
+              u32 cmp_imm_len = 1 << (len_field - 1);
+              u32 cmp_imm = decode_imm(ctx, cmp_imm_len); // 2nd imm, at worst 4 bytes past prog_len
               // cmp_imm is size in bytes of data to compare.
               // pc is offset of program bytes to compare.
               // imm is jump target offset.
               // REG is offset of packet bytes to compare.
-              if (len_field > 2) return PASS_PACKET; // guarantees cmp_imm <= 0xFFFF
+              if (cmp_imm > 0xFFFF) return PASS_PACKET;
               // pc < program_len < ram_len < 2GiB, thus pc + cmp_imm cannot wrap
               if (!IN_RAM_BOUNDS(ctx->pc + cmp_imm - 1)) return PASS_PACKET;
               ASSERT_IN_PACKET_BOUNDS(REG);