Support medium memory models.

With `-mcmodel=medium`, Clang may emit loads of the GOT address.
Delocate needs to handle that in order to avoid a relocation inside the
module.

Bug: b:316210772
Change-Id: I55eb2711860e43f68de131e28538aef9f5ce1889
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/64791
Auto-Submit: Adam Langley <agl@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

util/fipstools/delocate/delocate.go

@@ -1163,6 +1163,22 @@ Args:
 
 			args = append(args, argStr)
 
+		case ruleGOTAddress:
+			if instructionName != "leaq" {
+				return nil, fmt.Errorf("_GLOBAL_OFFSET_TABLE_ used outside of lea")
+			}
+			if i != 0 || len(argNodes) != 2 {
+				return nil, fmt.Errorf("Load of _GLOBAL_OFFSET_TABLE_ address didn't have expected form")
+			}
+			d.gotDeltaNeeded = true
+			changed = true
+			targetReg := d.contents(argNodes[1])
+			args = append(args, ".Lboringssl_got_delta(%rip)")
+			wrappers = append(wrappers, func(k func()) {
+				k()
+				d.output.WriteString(fmt.Sprintf("\taddq .Lboringssl_got_delta(%%rip), %s\n", targetReg))
+			})
+
 		case ruleGOTLocation:
 			if instructionName != "movabsq" {
 				return nil, fmt.Errorf("_GLOBAL_OFFSET_TABLE_ lookup didn't use movabsq")

util/fipstools/delocate/delocate.peg

@@ -68,8 +68,9 @@ LocalLabel <- [0-9][0-9$]*
 LocalLabelRef <- [0-9][0-9$]*[bf]
 Instruction <- InstructionName (WS InstructionArg ((WS? ',' WS?) InstructionArg)*)?
 InstructionName <- [[A-Z]][[A-Z.0-9]]* [.+\-]?
-InstructionArg <- IndirectionIndicator? (ARMConstantTweak / RegisterOrConstant / LocalLabelRef / TOCRefHigh / TOCRefLow / GOTLocation / GOTSymbolOffset / MemoryRef) AVX512Token*
+InstructionArg <- IndirectionIndicator? (ARMConstantTweak / RegisterOrConstant / LocalLabelRef / TOCRefHigh / TOCRefLow / GOTLocation / GOTAddress / GOTSymbolOffset / MemoryRef) AVX512Token*
 GOTLocation <- '$_GLOBAL_OFFSET_TABLE_-' LocalSymbol
+GOTAddress <- '_GLOBAL_OFFSET_TABLE_(%rip)'
 GOTSymbolOffset <- ('$' SymbolName '@GOT' 'OFF'?) / (":got:" SymbolName)
 AVX512Token <- WS? '{' '%'? [0-9a-z]* '}'
 TOCRefHigh <- '.TOC.-' ('0b' / ('.L' [a-zA-Z_0-9]+)) "@ha"