linux-kernel - [PATCH 2/2] riscv: introduce asm/flat.h

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Date:   Wed,  7 Apr 2021 20:56:38 +0900
From:   Damien Le Moal <damien.lemoal@....com>
To:     Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org
Cc:     Max Filippov <jcmvbkbc@...il.com>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Anup Patel <anup.patel@....com>, Christoph Hellwig <hch@....de>
Subject: [PATCH 2/2] riscv: introduce asm/flat.h

uclibc/gcc combined with elf2flt riscv linker file fully resolve the
PC relative __global_pointer$ value at compile time and do not generate
a relocation entry to set a runtime gp value. As a result, if the
flatbin loader introduces a gap between the text and data sections, the
gp value becomes incorrect and prevent correct execution of a flatbin
executable. Avoid this problem by introducing the file asm/flat.h
and defining the macro FLAT_TEXT_DATA_NO_GAP to indicate that the text
and data sections must be loaded at contiguous addresses.

Signed-off-by: Damien Le Moal <damien.lemoal@....com>
---
 arch/riscv/include/asm/Kbuild |  1 -
 arch/riscv/include/asm/flat.h | 29 +++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/include/asm/flat.h

diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
index 445ccc97305a..a8b54a3f4c2b 100644
--- a/arch/riscv/include/asm/Kbuild
+++ b/arch/riscv/include/asm/Kbuild
@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 generic-y += early_ioremap.h
 generic-y += extable.h
-generic-y += flat.h
 generic-y += kvm_para.h
 generic-y += user.h
 generic-y += vmlinux.lds.h
diff --git a/arch/riscv/include/asm/flat.h b/arch/riscv/include/asm/flat.h
new file mode 100644
index 000000000000..43bccf090fd1
--- /dev/null
+++ b/arch/riscv/include/asm/flat.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RISCV_FLAT_H
+#define _ASM_RISCV_FLAT_H
+
+#include <asm/unaligned.h>
+
+static inline int flat_get_addr_from_rp(u32 __user *rp, u32 relval, u32 flags,
+					u32 *addr)
+{
+	*addr = get_unaligned((__force u32 *)rp);
+	return 0;
+}
+
+static inline int flat_put_addr_at_rp(u32 __user *rp, u32 addr, u32 rel)
+{
+	put_unaligned(addr, (__force u32 *)rp);
+	return 0;
+}
+
+/*
+ * uclibc/gcc fully resolve the PC relative __global_pointer value
+ * at compile time and do not generate a relocation entry to set a
+ * runtime gp value. As a result, the flatbin loader must not introduce
+ * a gap between the text and data sections and keep them contiguous to
+ * avoid invalid address accesses.
+ */
+#define FLAT_TEXT_DATA_NO_GAP	(1)
+
+#endif /* _ASM_RISCV_FLAT_H */
-- 
2.30.2