[xen master] x86/setup: Rework cmdline_cook() to be compatible with -Wwrite-strings

[patchbot@xxxxxxx]

commit 858e3bf3493cc43e66acede71c3b159db0b82ef9
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Nov 20 22:10:59 2023 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Nov 23 11:20:01 2023 +0000

    x86/setup: Rework cmdline_cook() to be compatible with -Wwrite-strings
    
    Rework the logic in __start_xen() to not potentially pass NULL into
    cmdline_cook().  This makes the logic easier to follow too, and the rest of
    __start_xen() is safe when initialising cmdline to the empty string.
    
    Update cmdline_cook() to take and return const pointers, and write a
    description of what it does.  It now requires a non-NULL input and 
guarentees
    to return a pointer somewhere in the 'p' string.
    
    Note this only compiles because strstr() launders the const off the pointer
    when assigning to the mutable kextra, but that logic only mutates the
    mbi->cmdline buffer.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/setup.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 478107ef28..bf9da48060 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -839,10 +839,15 @@ static bool __init loader_is_grub2(const char 
*loader_name)
     return (p != NULL) && (p[5] != '0');
 }
 
-static char * __init cmdline_cook(char *p, const char *loader_name)
+/*
+ * Clean up a command line string passed to us by a bootloader.  Strip leading
+ * whitespace, and optionally strip the first parameter if our divination of
+ * the bootloader suggests that it prepended the image name.
+ *
+ * Always returns a pointer within @p.
+ */
+static const char *__init cmdline_cook(const char *p, const char *loader_name)
 {
-    p = p ? : "";
-
     /* Strip leading whitespace. */
     while ( *p == ' ' )
         p++;
@@ -971,8 +976,8 @@ static struct domain *__init create_dom0(const module_t 
*image,
 /* SAF-1-safe */
 void __init noreturn __start_xen(unsigned long mbi_p)
 {
-    const char *memmap_type = NULL, *loader;
-    char *cmdline, *kextra;
+    const char *memmap_type = NULL, *loader, *cmdline = "";
+    char *kextra;
     void *bsp_stack;
     struct cpu_info *info = get_cpu_info(), *bsp_info;
     unsigned int initrdidx, num_parked = 0;
@@ -1027,9 +1032,9 @@ void __init noreturn __start_xen(unsigned long mbi_p)
                                            : "unknown";
 
     /* Parse the command-line options. */
-    cmdline = cmdline_cook((mbi->flags & MBI_CMDLINE) ?
-                           __va(mbi->cmdline) : NULL,
-                           loader);
+    if ( mbi->flags & MBI_CMDLINE )
+        cmdline = cmdline_cook(__va(mbi->cmdline), loader);
+
     if ( (kextra = strstr(cmdline, " -- ")) != NULL )
     {
         /*
--
generated by git-patchbot for /home/xen/git/xen.git#master