libdrgn: add stub s390 and s390x architectures with relocation implementation

The only relocation type I saw in Debian's kernel module debug info was
R_390_32. R_390_8, R_390_16, R_390_64, R_390_PC16, R_390_PC32, and
R_390_PC64 are trivial to support, as well. The Linux kernel supports
many more, but hopefully they won't show up for debug info.

Signed-off-by: Omar Sandoval <osandov@osandov.com>

_drgn.pyi

@@ -954,6 +954,12 @@ class Architecture(enum.Enum):
     RISCV32 = ...
     """The 32-bit RISC-V architecture."""
 
+    S390X = ...
+    """The s390x architecture, a.k.a. IBM Z or z/Architecture."""
+
+    S390 = ...
+    """The 32-bit s390 architecture, a.k.a. System/390."""
+
     UNKNOWN = ...
     """
     An architecture which is not known to drgn. Certain features are not

libdrgn/Makefile.am

@@ -35,6 +35,7 @@ libdrgnimpl_la_SOURCES = $(ARCH_DEFS_PYS:_defs.py=.c) \
 			 arch_arm.c \
 			 arch_i386.c \
 			 arch_riscv.c \
+			 arch_s390x.c \
 			 array.h \
 			 binary_buffer.c \
 			 binary_buffer.h \

libdrgn/arch_s390x.c

@@ -0,0 +1,57 @@
+// Copyright (c) Meta Platforms, Inc. and affiliates.
+// SPDX-License-Identifier: LGPL-2.1-or-later
+
+#include "platform.h" // IWYU pragma: associated
+
+static struct drgn_error *
+apply_elf_reloc_s390(const struct drgn_relocating_section *relocating,
+		     uint64_t r_offset, uint32_t r_type,
+		     const int64_t *r_addend, uint64_t sym_value)
+{
+	switch (r_type) {
+	case R_390_NONE:
+		return NULL;
+	case R_390_8:
+		return drgn_reloc_add8(relocating, r_offset, r_addend,
+				       sym_value);
+	case R_390_16:
+		return drgn_reloc_add16(relocating, r_offset, r_addend,
+					sym_value);
+	case R_390_32:
+		return drgn_reloc_add32(relocating, r_offset, r_addend,
+					sym_value);
+	case R_390_PC32:
+		return drgn_reloc_add32(relocating, r_offset, r_addend,
+					sym_value
+					- (relocating->addr + r_offset));
+	case R_390_PC16:
+		return drgn_reloc_add16(relocating, r_offset, r_addend,
+					sym_value
+					- (relocating->addr + r_offset));
+	case R_390_64:
+		return drgn_reloc_add64(relocating, r_offset, r_addend,
+					sym_value);
+	case R_390_PC64:
+		return drgn_reloc_add64(relocating, r_offset, r_addend,
+					sym_value
+					- (relocating->addr + r_offset));
+	default:
+		return DRGN_UNKNOWN_RELOCATION_TYPE(r_type);
+	}
+}
+
+const struct drgn_architecture_info arch_info_s390x = {
+	.name = "s390x",
+	.arch = DRGN_ARCH_S390X,
+	.default_flags = DRGN_PLATFORM_IS_64_BIT,
+	.register_by_name = drgn_register_by_name_unknown,
+	.apply_elf_reloc = apply_elf_reloc_s390,
+};
+
+const struct drgn_architecture_info arch_info_s390 = {
+	.name = "s390",
+	.arch = DRGN_ARCH_S390,
+	.default_flags = 0,
+	.register_by_name = drgn_register_by_name_unknown,
+	.apply_elf_reloc = apply_elf_reloc_s390,
+};

libdrgn/drgn.h.in

@@ -375,6 +375,8 @@ enum drgn_architecture {
 	DRGN_ARCH_PPC64,
 	DRGN_ARCH_RISCV64,
 	DRGN_ARCH_RISCV32,
+	DRGN_ARCH_S390X,
+	DRGN_ARCH_S390,
 };
 
 /** Flags describing a @ref drgn_platform. */

libdrgn/kdump.c

@@ -36,6 +36,10 @@ static struct drgn_error *drgn_platform_from_kdump(kdump_ctx_t *ctx,
 	else if (strcmp(str, KDUMP_ARCH_PPC64) == 0)
 		arch = &arch_info_ppc64;
 	/* libkdumpfile doesn't support RISC-V */
+	else if (strcmp(str, KDUMP_ARCH_S390X) == 0)
+		arch = &arch_info_s390x;
+	else if (strcmp(str, KDUMP_ARCH_S390) == 0)
+		arch = &arch_info_s390;
 	else
 		arch = &arch_info_unknown;
 

libdrgn/platform.c

@@ -38,6 +38,11 @@ LIBDRGN_PUBLIC const struct drgn_platform drgn_host_platform = {
 #else
 #error "unknown __riscv_xlen"
 #endif
+#elif __s390x__
+	.arch = &arch_info_s390x,
+// __s390__ is also defined for s390x, so the order is important.
+#elif __s390__
+	.arch = &arch_info_s390,
 #else
 	.arch = &arch_info_unknown,
 #endif
@@ -77,6 +82,12 @@ drgn_platform_create(enum drgn_architecture arch,
 	case DRGN_ARCH_RISCV32:
 		arch_info = &arch_info_riscv32;
 		break;
+	case DRGN_ARCH_S390X:
+		arch_info = &arch_info_s390x;
+		break;
+	case DRGN_ARCH_S390:
+		arch_info = &arch_info_s390;
+		break;
 	default:
 		return drgn_error_create(DRGN_ERROR_INVALID_ARGUMENT,
 					 "invalid architecture");
@@ -162,6 +173,12 @@ void drgn_platform_from_elf(GElf_Ehdr *ehdr, struct drgn_platform *ret)
 		else
 			arch = &arch_info_riscv32;
 		break;
+	case EM_S390:
+		if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
+			arch = &arch_info_s390x;
+		else
+			arch = &arch_info_s390;
+		break;
 	default:
 		arch = &arch_info_unknown;
 		break;

libdrgn/platform.h

@@ -372,6 +372,8 @@ extern const struct drgn_architecture_info arch_info_arm;
 extern const struct drgn_architecture_info arch_info_ppc64;
 extern const struct drgn_architecture_info arch_info_riscv64;
 extern const struct drgn_architecture_info arch_info_riscv32;
+extern const struct drgn_architecture_info arch_info_s390x;
+extern const struct drgn_architecture_info arch_info_s390;
 
 struct drgn_platform {
 	const struct drgn_architecture_info *arch;