Merge patch series "riscv: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION"

Jisheng Zhang <jszhang@kernel.org> says:

When trying to run linux with various opensource riscv core on
resource limited FPGA platforms, for example, those FPGAs with less
than 16MB SDRAM, I want to save mem as much as possible. One of the
major technologies is kernel size optimizations, I found that riscv
does not currently support HAVE_LD_DEAD_CODE_DATA_ELIMINATION, which
passes -fdata-sections, -ffunction-sections to CFLAGS and passes the
--gc-sections flag to the linker.

This not only benefits my case on FPGA but also benefits defconfigs.
Here are some notable improvements from enabling this with defconfigs:

nommu_k210_defconfig:
   text    data     bss     dec     hex
1112009  410288   59837 1582134  182436     before
 962838  376656   51285 1390779  1538bb     after

rv32_defconfig:
   text    data     bss     dec     hex
8804455 2816544  290577 11911576 b5c198     before
8692295 2779872  288977 11761144 b375f8     after

defconfig:
   text    data     bss     dec     hex
9438267 3391332  485333 13314932 cb2b74     before
9285914 3350052  483349 13119315 c82f53     after

patch1 and patch2 are clean ups.
patch3 fixes a typo.
patch4 finally enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION for riscv.

* b4-shazam-merge:
  riscv: disable HAVE_LD_DEAD_CODE_DATA_ELIMINATION for LLD
  riscv: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION
  vmlinux.lds.h: use correct .init.data.* section name
  riscv: vmlinux-xip.lds.S: remove .alternative section
  riscv: move options to keep entries sorted
  riscv: Fix orphan section warnings caused by kernel/pi

Link: https://lore.kernel.org/r/20230523165502.2592-1-jszhang@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

3 files changed, 11 insertions, 15 deletions

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 08f3a01fa1ea..c8c22cf11602 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -105,6 +105,11 @@ config RISCV
 	select HAVE_CONTEXT_TRACKING_USER
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS if MMU
+	select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE)
+	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
+	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
+	select HAVE_FUNCTION_GRAPH_TRACER
+	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
 	select HAVE_EBPF_JIT if MMU
 	select HAVE_FUNCTION_ARG_ACCESS_API
 	select HAVE_FUNCTION_ERROR_INJECTION
@@ -114,7 +119,8 @@ config RISCV
 	select HAVE_KPROBES if !XIP_KERNEL
 	select HAVE_KPROBES_ON_FTRACE if !XIP_KERNEL
 	select HAVE_KRETPROBES if !XIP_KERNEL
-	select HAVE_RETHOOK if !XIP_KERNEL
+	# https://github.com/ClangBuiltLinux/linux/issues/1881
+	select HAVE_LD_DEAD_CODE_DATA_ELIMINATION if !LD_IS_LLD
 	select HAVE_MOVE_PMD
 	select HAVE_MOVE_PUD
 	select HAVE_PCI
@@ -123,6 +129,7 @@ config RISCV
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_POSIX_CPU_TIMERS_TASK_WORK
 	select HAVE_REGS_AND_STACK_ACCESS_API
+	select HAVE_RETHOOK if !XIP_KERNEL
 	select HAVE_RSEQ
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
@@ -148,11 +155,6 @@ config RISCV
 	select TRACE_IRQFLAGS_SUPPORT
 	select UACCESS_MEMCPY if !MMU
 	select ZONE_DMA32 if 64BIT
-	select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE)
-	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
-	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
-	select HAVE_FUNCTION_GRAPH_TRACER
-	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
 
 config CLANG_SUPPORTS_DYNAMIC_FTRACE
 	def_bool CC_IS_CLANG
diff --git a/arch/riscv/kernel/vmlinux-xip.lds.S b/arch/riscv/kernel/vmlinux-xip.lds.S
index eab9edc3b631..50767647fbc6 100644
--- a/arch/riscv/kernel/vmlinux-xip.lds.S
+++ b/arch/riscv/kernel/vmlinux-xip.lds.S
@@ -98,12 +98,6 @@ SECTIONS
 		__soc_builtin_dtb_table_end = .;
 	}
 
-	. = ALIGN(8);
-	.alternative : {
-		__alt_start = .;
-		*(.alternative)
-		__alt_end = .;
-	}
 	__init_end = .;
 
 	. = ALIGN(16);
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index e5f9f4677bbf..492dd4b8f3d6 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -85,11 +85,11 @@ SECTIONS
 	INIT_DATA_SECTION(16)
 
 	.init.pi : {
-		*(.init.pi*)
+		KEEP(*(.init.pi*))
 	}
 
 	.init.bss : {
-		*(.init.bss)	/* from the EFI stub */
+		KEEP(*(.init.bss*))	/* from the EFI stub */
 	}
 	.exit.data :
 	{
@@ -112,7 +112,7 @@ SECTIONS
 	. = ALIGN(8);
 	.alternative : {
 		__alt_start = .;
-		*(.alternative)
+		KEEP(*(.alternative))
 		__alt_end = .;
 	}
 	__init_end = .;