diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -422,11 +422,11 @@
          s == "nodelete" || s == "nodlopen" || s == "noexecstack" ||
          s == "nognustack" || s == "nokeep-text-section-prefix" ||
          s == "norelro" || s == "noseparate-code" || s == "notext" ||
-         s == "now" || s == "origin" || s == "pac-plt" || s == "relro" ||
-         s == "retpolineplt" || s == "rodynamic" || s == "shstk" ||
-         s == "text" || s == "undefs" || s == "wxneeded" ||
-         s.startswith("common-page-size=") || s.startswith("max-page-size=") ||
-         s.startswith("stack-size=");
+         s == "now" || s == "origin" || s == "pac-plt" || s == "rel" ||
+         s == "rela" || s == "relro" || s == "retpolineplt" ||
+         s == "rodynamic" || s == "shstk" || s == "text" || s == "undefs" ||
+         s == "wxneeded" || s.startswith("common-page-size=") ||
+         s.startswith("max-page-size=") || s.startswith("stack-size=");
 }
 
 // Report an error for an unknown -z option.
@@ -842,6 +842,22 @@
   return names.takeVector();
 }
 
+static bool getIsRela(opt::InputArgList &args) {
+  // If -z rel or -z rela is specified, use the last option.
+  for (auto *arg : args.filtered_reverse(OPT_z)) {
+    StringRef s(arg->getValue());
+    if (s == "rel")
+      return false;
+    if (s == "rela")
+      return true;
+  }
+
+  // Otherwise use the psABI defined relocation entry format.
+  uint16_t m = config->emachine;
+  return m == EM_AARCH64 || m == EM_AMDGPU || m == EM_HEXAGON || m == EM_PPC ||
+         m == EM_PPC64 || m == EM_RISCV || m == EM_X86_64;
+}
+
 static void parseClangOption(StringRef opt, const Twine &msg) {
   std::string err;
   raw_string_ostream os(err);
@@ -1204,20 +1220,19 @@
 
   // ELF defines two different ways to store relocation addends as shown below:
   //
-  //  Rel:  Addends are stored to the location where relocations are applied.
+  //  Rel: Addends are stored to the location where relocations are applied. It
+  //  cannot pack the full range of addend values for all relocation types, but
+  //  this only affects relocation types that we don't support emitting as
+  //  dynamic relocations (see getDynRel).
   //  Rela: Addends are stored as part of relocation entry.
   //
   // In other words, Rela makes it easy to read addends at the price of extra
-  // 4 or 8 byte for each relocation entry. We don't know why ELF defined two
-  // different mechanisms in the first place, but this is how the spec is
-  // defined.
+  // 4 or 8 byte for each relocation entry.
   //
-  // You cannot choose which one, Rel or Rela, you want to use. Instead each
-  // ABI defines which one you need to use. The following expression expresses
-  // that.
-  config->isRela = m == EM_AARCH64 || m == EM_AMDGPU || m == EM_HEXAGON ||
-                   m == EM_PPC || m == EM_PPC64 || m == EM_RISCV ||
-                   m == EM_X86_64;
+  // We pick the format for dynamic relocations according to the psABI for each
+  // processor, but a contrary choice can be made if the dynamic loader
+  // supports.
+  config->isRela = getIsRela(args);
 
   // If the output uses REL relocations we must store the dynamic relocation
   // addends to the output sections. We also store addends for RELA relocations
diff --git a/lld/docs/ld.lld.1 b/lld/docs/ld.lld.1
--- a/lld/docs/ld.lld.1
+++ b/lld/docs/ld.lld.1
@@ -720,6 +720,12 @@
 .It Cm pac-plt
 AArch64 only, use pointer authentication in PLT.
 .Pp
+.It Cm rel
+Use REL format for dynamic relocations.
+.Pp
+.It Cm rela
+Use RELA format for dynamic relocations.
+.Pp
 .It Cm retpolineplt
 Emit retpoline format PLT entries as a mitigation for CVE-2017-5715.
 .Pp
diff --git a/lld/test/ELF/i386-zrel-zrela.s b/lld/test/ELF/i386-zrel-zrela.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/i386-zrel-zrela.s
@@ -0,0 +1,63 @@
+# REQUIRES: x86
+## The i386 psABI uses Elf64_Rela relocation entries. We produce
+## Elf32_Rel dynamic relocations by default, but can use Elf32_Rela with -z rela.
+
+# RUN: llvm-mc -filetype=obj -triple=i386 %s -o %t.o
+# RUN: ld.lld -shared %t.o -o %t.so
+# RUN: llvm-readobj -d -r -x .data %t.so | FileCheck --check-prefix=REL %s
+# RUN: ld.lld -shared -z rel %t.o -o %t1.so
+# RUN: llvm-readobj -d -r -x .data %t1.so | FileCheck --check-prefix=REL %s
+
+# REL:      REL      {{.*}}
+# REL-NEXT: RELSZ    32 (bytes)
+# REL-NEXT: RELENT   8 (bytes)
+# REL-NEXT: RELCOUNT 1
+# REL-NEXT: JMPREL   {{.*}}
+# REL-NEXT: PLTRELSZ 8 (bytes)
+# REL-NEXT: PLTGOT   {{.*}}
+# REL-NEXT: PLTREL   REL{{$}}
+# REL:      .rel.dyn {
+# REL-NEXT:   R_386_RELATIVE - 0x0
+# REL-NEXT:   R_386_GLOB_DAT func 0x0
+# REL-NEXT:   R_386_TLS_TPOFF tls 0x0
+# REL-NEXT:   R_386_32 _start 0x0
+# REL-NEXT: }
+# REL-NEXT: .rel.plt {
+# REL-NEXT:   R_386_JUMP_SLOT func 0x0
+# REL-NEXT: }
+
+# REL:      Hex dump of section '.data':
+# REL-NEXT: 0x000042cc cc420000 2a000000
+
+# RUN: ld.lld -shared -z rel -z rela %t.o -o %t2.so
+# RUN: llvm-readobj -d -r %t2.so | FileCheck --check-prefix=RELA %s
+
+# RELA:      RELA      {{.*}}
+# RELA-NEXT: RELASZ    48 (bytes)
+# RELA-NEXT: RELAENT   12 (bytes)
+# RELA-NEXT: RELACOUNT 1
+# RELA-NEXT: JMPREL    {{.*}}
+# RELA-NEXT: PLTRELSZ  12 (bytes)
+# RELA-NEXT: PLTGOT    {{.*}}
+# RELA-NEXT: PLTREL    RELA
+# RELA:      .rela.dyn {
+# RELA-NEXT:   R_386_RELATIVE - 0x42EC
+# RELA-NEXT:   R_386_GLOB_DAT func 0x0
+# RELA-NEXT:   R_386_TLS_TPOFF tls 0x2A
+# RELA-NEXT:   R_386_32 _start 0x2A
+# RELA-NEXT: }
+# RELA-NEXT: .rela.plt {
+# RELA-NEXT:   R_386_JUMP_SLOT func 0x0
+# RELA-NEXT: }
+
+.globl _start
+_start:
+  call func@PLT
+  movl func@GOT(%eax), %eax
+
+.section .text1,"awx"
+  movl %gs:tls@NTPOFF+42, %eax
+
+.data
+  .long .data
+  .long _start+42
diff --git a/lld/test/ELF/x86-64-zrel-zrela.s b/lld/test/ELF/x86-64-zrel-zrela.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/x86-64-zrel-zrela.s
@@ -0,0 +1,58 @@
+# REQUIRES: x86
+## The x86-64 psABI uses Elf64_Rela relocation entries. We produce
+## Elf64_Rel dynamic relocations by default, but can use Elf64_Rel with -z rel.
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o
+# RUN: ld.lld -shared %t.o -o %t.so
+# RUN: llvm-readobj -d -r %t.so | FileCheck --check-prefix=RELA %s
+# RUN: ld.lld -shared -z rela %t.o -o %t1.so
+# RUN: llvm-readobj -d -r %t1.so | FileCheck --check-prefix=RELA %s
+
+# RELA:      RELA      {{.*}}
+# RELA-NEXT: RELASZ    72 (bytes)
+# RELA-NEXT: RELAENT   24 (bytes)
+# RELA-NEXT: RELACOUNT 1
+# RELA-NEXT: JMPREL    {{.*}}
+# RELA-NEXT: PLTRELSZ  24 (bytes)
+# RELA-NEXT: PLTGOT    {{.*}}
+# RELA-NEXT: PLTREL    RELA
+# RELA:      .rela.dyn {
+# RELA-NEXT:   R_X86_64_RELATIVE - 0x3428
+# RELA-NEXT:   R_X86_64_GLOB_DAT func 0x0
+# RELA-NEXT:   R_X86_64_64 _start 0x2A
+# RELA-NEXT: }
+# RELA-NEXT: .rela.plt {
+# RELA-NEXT:   R_X86_64_JUMP_SLOT func 0x0
+# RELA-NEXT: }
+
+# RUN: ld.lld -shared -z rela -z rel %t.o -o %t2.so
+# RUN: llvm-readobj -d -r -x .data %t2.so | FileCheck --check-prefix=REL %s
+
+# REL:      REL      {{.*}}
+# REL-NEXT: RELSZ    48 (bytes)
+# REL-NEXT: RELENT   16 (bytes)
+# REL-NEXT: RELCOUNT 1
+# REL-NEXT: JMPREL   {{.*}}
+# REL-NEXT: PLTRELSZ 16 (bytes)
+# REL-NEXT: PLTGOT   {{.*}}
+# REL-NEXT: PLTREL   REL{{$}}
+# REL:      .rel.dyn {
+# REL-NEXT:   R_X86_64_RELATIVE - 0x0
+# REL-NEXT:   R_X86_64_GLOB_DAT func 0x0
+# REL-NEXT:   R_X86_64_64 _start 0
+# REL-NEXT: }
+# REL-NEXT: .rel.plt {
+# REL-NEXT:   R_X86_64_JUMP_SLOT func 0x0
+# REL-NEXT: }
+
+# REL:      Hex dump of section '.data':
+# REL-NEXT: 0x00003408 08340000 00000000 2a000000 00000000
+
+.globl _start
+_start:
+  call func@PLT
+  movq func@GOTPCREL(%rip), %rax
+
+.data
+  .quad .data
+  .quad _start+42