[BPF] printk gets fmt from .rodata instead of stack

Instead of creating the string on stack before every printk call,
declaring it static const places is in .rodata where from kernel 5.2+
can get it. That saves some instructions for each printk call and
reduces binary size.

Based on this blog: https://nakryiko.com/posts/bpf-tips-printk/

Before:

0000000000000000 <calico_tc_v6>:
       0:       bf 19 00 00 00 00 00 00 r9 = r1
       1:       b7 01 00 00 61 6d 0a 00 r1 = 683361
       2:       63 1a e8 ff 00 00 00 00 *(u32 *)(r10 - 24) = r1
       3:       18 01 00 00 75 65 20 70 00 00 00 00 72 6f 67 72 r1 = 8243680180223108469 ll
       5:       7b 1a e0 ff 00 00 00 00 *(u64 *)(r10 - 32) = r1
       6:       18 01 00 00 36 20 70 72 00 00 00 00 6f 6c 6f 67 r1 = 7453295134238580790 ll
       8:       7b 1a d8 ff 00 00 00 00 *(u64 *)(r10 - 40) = r1
       9:       18 01 00 00 72 69 6e 67 00 00 00 00 20 49 50 76 r1 = 8525394498135419250 ll
      11:       7b 1a d0 ff 00 00 00 00 *(u64 *)(r10 - 48) = r1
      12:       18 01 00 00 2d 49 3a 20 00 00 00 00 45 6e 74 65 r1 = 7310589338301647149 ll
      14:       7b 1a c8 ff 00 00 00 00 *(u64 *)(r10 - 56) = r1
      15:       18 06 00 00 43 41 4c 49 00 00 00 00 43 4f 4c 4f r6 = 5714029177637454147 ll
      17:       7b 6a c0 ff 00 00 00 00 *(u64 *)(r10 - 64) = r6
      18:       bf a1 00 00 00 00 00 00 r1 = r10
      19:       07 01 00 00 c0 ff ff ff r1 += -64
      20:       b7 02 00 00 2c 00 00 00 r2 = 44
      21:       85 00 00 00 06 00 00 00 call 6
      22:       b7 08 00 00 00 00 00 00 r8 = 0
      23:       63 8a c0 ff 00 00 00 00 *(u32 *)(r10 - 64) = r8
      24:       bf a2 00 00 00 00 00 00 r2 = r10
      25:       07 02 00 00 c0 ff ff ff r2 += -64
      26:       18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll
      28:       85 00 00 00 01 00 00 00 call 1
      29:       bf 07 00 00 00 00 00 00 r7 = r0
      30:       63 8a c0 ff 00 00 00 00 *(u32 *)(r10 - 64) = r8
      31:       bf a2 00 00 00 00 00 00 r2 = r10
      32:       07 02 00 00 c0 ff ff ff r2 += -64
      33:       18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll
      35:       85 00 00 00 01 00 00 00 call 1
      36:       55 07 14 00 00 00 00 00 if r7 != 0 goto +20 <LBB0_2>
      37:       73 8a ea ff 00 00 00 00 *(u8 *)(r10 - 22) = r8
      38:       b7 01 00 00 50 0a 00 00 r1 = 2640
      39:       6b 1a e8 ff 00 00 00 00 *(u16 *)(r10 - 24) = r1
      40:       18 01 00 00 6c 65 64 3a 00 00 00 00 20 44 52 4f r1 = 5715705782295881068 ll
      42:       7b 1a e0 ff 00 00 00 00 *(u64 *)(r10 - 32) = r1
      43:       18 01 00 00 6f 6b 75 70 00 00 00 00 20 66 61 69 r1 = 7593462736235096943 ll
      45:       7b 1a d8 ff 00 00 00 00 *(u64 *)(r10 - 40) = r1
      46:       18 01 00 00 65 20 6d 61 00 00 00 00 70 20 6c 6f r1 = 8028827902737719397 ll
      48:       7b 1a d0 ff 00 00 00 00 *(u64 *)(r10 - 48) = r1
      49:       18 01 00 00 2d 49 3a 20 00 00 00 00 53 74 61 74 r1 = 8386111881512372525 ll
      51:       7b 1a c8 ff 00 00 00 00 *(u64 *)(r10 - 56) = r1
      52:       7b 6a c0 ff 00 00 00 00 *(u64 *)(r10 - 64) = r6
      53:       bf a1 00 00 00 00 00 00 r1 = r10
      54:       07 01 00 00 c0 ff ff ff r1 += -64
      55:       b7 02 00 00 2b 00 00 00 r2 = 43
      56:       05 00 6f 00 00 00 00 00 goto +111 <LBB0_10>

After:

0000000000000000 <calico_tc_v6>:
       0:       bf 16 00 00 00 00 00 00 r6 = r1
       1:       18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll
       3:       b7 02 00 00 2c 00 00 00 r2 = 44
       4:       85 00 00 00 06 00 00 00 call 6
       5:       b7 08 00 00 00 00 00 00 r8 = 0
       6:       63 8a f8 ff 00 00 00 00 *(u32 *)(r10 - 8) = r8
       7:       bf a2 00 00 00 00 00 00 r2 = r10
       8:       07 02 00 00 f8 ff ff ff r2 += -8
       9:       18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll
      11:       85 00 00 00 01 00 00 00 call 1
      12:       bf 07 00 00 00 00 00 00 r7 = r0
      13:       63 8a f8 ff 00 00 00 00 *(u32 *)(r10 - 8) = r8
      14:       bf a2 00 00 00 00 00 00 r2 = r10
      15:       07 02 00 00 f8 ff ff ff r2 += -8
      16:       18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll
      18:       85 00 00 00 01 00 00 00 call 1
      19:       bf 08 00 00 00 00 00 00 r8 = r0
      20:       55 07 04 00 00 00 00 00 if r7 != 0 goto +4 <LBB0_2>
      21:       18 01 00 00 2c 00 00 00 00 00 00 00 00 00 00 00 r1 = 44 ll
      23:       b7 02 00 00 2b 00 00 00 r2 = 43
      24:       05 00 2d 00 00 00 00 00 goto +45 <LBB0_11>

felix/bpf-gpl/log.h

@@ -24,7 +24,7 @@
 
 #ifdef BPF_CORE_SUPPORTED
 #define bpf_log(__fmt, ...) do { \
-		char fmt[] = IPVER_PFX __fmt; \
+		static const char fmt[] = IPVER_PFX __fmt; \
 		bpf_trace_printk(fmt, sizeof(fmt), ## __VA_ARGS__); \
 } while (0)
 #else

felix/bpf/hook/map.go

@@ -145,7 +145,7 @@ func (pm *ProgramsMap) loadObj(at AttachType, file string) (Layout, error) {
 
 	for m, err := obj.FirstMap(); m != nil && err == nil; m, err = m.NextMap() {
 		mapName := m.Name()
-		if strings.HasPrefix(mapName, ".rodata") {
+		if strings.Contains(mapName, ".rodata") {
 			continue
 		}
 

felix/bpf/nat/connecttime.go

@@ -132,7 +132,7 @@ func loadProgram(logLevel, ipver string, udpNotSeen time.Duration, excludeUDP bo
 		// userspace before the program is loaded.
 		mapName := m.Name()
 		if m.IsMapInternal() {
-			if strings.HasPrefix(mapName, ".rodata") {
+			if strings.Contains(mapName, ".rodata") {
 				continue
 			}
 			if err := libbpf.CTLBSetGlobals(m, udpNotSeen, excludeUDP); err != nil {