ZC: fix issue openhwgroup#55.

GAS tries to relax a conditional branch by flipping the condition bit and setting the offset to a two-instruction-length constant. relax bne t5,t3,.Lfar_away to beq t5,t3,8 # a constant value j .Lfar_away To solve this issue, we add a local symbol right after the `j` instruction, and then the linker can help adjust bytes during linker relaxation.
edward-jones · Jul 21, 2023 · c549628 · c549628
1 parent 02ec8cd
commit c549628
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Showing 4 changed files with 93 additions and 2 deletions.
diff --git a/gas/config/tc-riscv.c b/gas/config/tc-riscv.c
@@ -5328,7 +5328,24 @@ md_convert_frag_branch (fragS *fragp)
 	    /* Invert the branch condition.  Branch over the jump.  */
 	    insn = bfd_getl16 (buf);
 	    insn ^= MATCH_C_BEQZ ^ MATCH_C_BNEZ;
-	    insn |= ENCODE_CBTYPE_IMM (6);
+
+	    if (riscv_subset_supports (&riscv_rps_as, "zcmt"))
+	      {
+		symbolS *sym = symbol_new (FAKE_LABEL_NAME , now_seg, fragp,
+				     fragp->fr_fix + fragp->fr_var);
+		fixp = fix_new (fragp,
+				buf - (bfd_byte *)fragp->fr_literal,
+				2,
+				sym,
+				0,
+				false,
+				BFD_RELOC_RISCV_RVC_BRANCH);
+		fixp->fx_file = fragp->fr_file;
+		fixp->fx_line = fragp->fr_line;
+	      }
+	    else
+	      insn |= ENCODE_CBTYPE_IMM (6);
+
 	    bfd_putl16 (insn, buf);
 	    buf += 2;
 	    goto jump;
@@ -5355,7 +5372,25 @@ md_convert_frag_branch (fragS *fragp)
       /* Invert the branch condition.  Branch over the jump.  */
       insn = bfd_getl32 (buf);
       insn ^= MATCH_BEQ ^ MATCH_BNE;
-      insn |= ENCODE_BTYPE_IMM (8);
+
+      if (riscv_subset_supports (&riscv_rps_as, "zcmt"))
+	{
+	  symbolS *sym = (symbolS *) local_symbol_make (
+		    FAKE_LABEL_NAME, now_seg, fragp,
+		    fragp->fr_fix + fragp->fr_var);
+	  fixp = fix_new (fragp,
+			  buf - (bfd_byte *)fragp->fr_literal,
+			  4,
+			  sym,
+			  0,
+			  false,
+			  BFD_RELOC_12_PCREL);
+	  fixp->fx_file = fragp->fr_file;
+	  fixp->fx_line = fragp->fr_line;
+	}
+      else
+	insn |= ENCODE_BTYPE_IMM (8);
+
       bfd_putl32 (insn, buf);
       buf += 4;
 

diff --git a/gas/testsuite/gas/riscv/zc-zcmt-relax-branch.d b/gas/testsuite/gas/riscv/zc-zcmt-relax-branch.d
@@ -0,0 +1,19 @@
+#as: -march=rv32g_zca_zcmt
+#source: zc-zcmt-relax-branch.s
+#objdump: -dr -Mno-aliases
+
+.*:[	 ]+file format .*
+
+
+Disassembly of section .text:
+
+0+000 <target>:
+[	 ]*[0-9a-f]+:[	 ]+00940263[	 ]+beq[	 ]+s0,s1,4.+
+[^:]+: R_RISCV_BRANCH[	]+NORMAL
+
+0+4 <NORMAL>:
+[	 ]*[0-9a-f]+:[	 ]+00941463[	 ]+bne[	 ]+s0,s1,c.+
+[^:]+: R_RISCV_BRANCH[	]+\.L0
+[	 ]*[0-9a-f]+:[	 ]+0000006f[	 ]+jal[	 ]+zero,8.+
+[^:]+: R_RISCV_JAL[	]+\*ABS\*\-0x4
+[	 ]*[0-9a-f]+:[	 ]+8082[	 ]+c.jr[	 ]+ra
diff --git a/gas/testsuite/gas/riscv/zc-zcmt-relax-branch.s b/gas/testsuite/gas/riscv/zc-zcmt-relax-branch.s
@@ -0,0 +1,6 @@
+.option norelax
+target:
+	beq s0,s1,NORMAL
+NORMAL:
+	beq s0,s1,-4
+	ret
diff --git a/gas/testsuite/gas/riscv/zc-zcmt-relax-c-branch.d b/gas/testsuite/gas/riscv/zc-zcmt-relax-c-branch.d
@@ -0,0 +1,31 @@
+#as: -march=rv32g_zca_zcmt
+#source: zc-zcmt-relax-c-branch.s
+#objdump: -dr -Mno-aliases
+
+.*:[	 ]+file format .*
+
+
+Disassembly of section .text:
+
+0+000 <target>:
+[	 ]*[0-9a-f]+:[	 ]+c009[	 ]+c.beqz[	 ]+s0,2.+
+[^:]+: R_RISCV_RVC_BRANCH[	]+C_BRANCH_RANGE
+
+0+2 <C_BRANCH_RANGE>:
+[	 ]*[0-9a-f]+:[	 ]+10041263[	 ]+bne[	 ]+s0,zero,106.+
+[^:]+: R_RISCV_BRANCH[	]+EXPAND_TO_BRANCH
+#...
+
+.+ <EXPAND_TO_BRANCH>:
+[	 ]*[0-9a-f]+:[	 ]+c019[	 ]+c.beqz[	 ]+s0,10c.+
+[^:]+: R_RISCV_RVC_BRANCH[	]+\.L0
+[	 ]*[0-9a-f]+:[	 ]+0040106f[	 ]+jal[	 ]+zero,110c.+
+[^:]+: R_RISCV_JAL[	]+FLIP_C_BRANCH_AND_JUMP
+#...
+
+.+ <FLIP_C_BRANCH_AND_JUMP>:
+[	 ]*[0-9a-f]+:[	 ]+00041463[	 ]+bne[	 ]+s0,zero,1114.+
+[^:]+: R_RISCV_BRANCH[	]+\.L0
+[	 ]*[0-9a-f]+:[	 ]+0000006f[	 ]+jal[	 ]+zero,1110.+
+[^:]+: R_RISCV_JAL[	]+\*ABS\*\-0x4
+[	 ]*[0-9a-f]+:[	 ]+8082[	 ]+c.jr[	 ]+ra